Commit Graph

205 Commits

Author SHA1 Message Date
Milos Vyletel
ed38446424 documentation: State that rcu_dereference() reloads pointer
Make a note stating that repeated calls of rcu_dereference() may not
return the same pointer if update happens while in critical section.

Reported-by: Jeff Haran <jeff.haran@citrix.com>
Signed-off-by: Milos Vyletel <milos@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-05-27 12:57:28 -07:00
Paul E. McKenney
ee7c29be36 documentation: Update rcu_dereference.txt based on WG21 discussions
This commit provides another caveat for the care and feeding of pointers
returned by rcu_dereference() that was pointed out in discussions within
the C++ standards committee.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2015-05-27 12:57:28 -07:00
Paul E. McKenney
cf9fbf8017 documentation: RCU-protected array indexes no longer supported
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-05-27 12:56:17 -07:00
Paul E. McKenney
78e691f4ae Merge branches 'doc.2015.01.07a', 'fixes.2015.01.15a', 'preempt.2015.01.06a', 'srcu.2015.01.06a', 'stall.2015.01.16a' and 'torture.2015.01.11a' into HEAD
doc.2015.01.07a: Documentation updates.
fixes.2015.01.15a: Miscellaneous fixes.
preempt.2015.01.06a: Changes to handling of lists of preempted tasks.
srcu.2015.01.06a: SRCU updates.
stall.2015.01.16a: RCU CPU stall-warning updates and fixes.
torture.2015.01.11a: RCU torture-test updates and fixes.
2015-01-15 23:34:34 -08:00
Paul E. McKenney
fb81a44b88 rcu: Add GP-kthread-starvation checks to CPU stall warnings
This commit adds a message that is printed if the relevant grace-period
kthread has not been able to run for the two seconds preceding the
stall warning.  (The two seconds is double the maximum interval between
successive bouts of quiescent-state forcing.)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-15 23:33:15 -08:00
Paul E. McKenney
5cd37193ce rcu: Make cond_resched_rcu_qs() apply to normal RCU flavors
Although cond_resched_rcu_qs() only applies to TASKS_RCU, it is used
in places where it would be useful for it to apply to the normal RCU
flavors, rcu_preempt, rcu_sched, and rcu_bh.  This is especially the
case for workloads that aggressively overload the system, particularly
those that generate large numbers of RCU updates on systems running
NO_HZ_FULL CPUs.  This commit therefore communicates quiescent states
from cond_resched_rcu_qs() to the normal RCU flavors.

Note that it is unfortunately necessary to leave the old ->passed_quiesce
mechanism in place to allow quiescent states that apply to only one
flavor to be recorded.  (Yes, we could decrement ->rcu_qs_ctr_snap in
that case, but that is not so good for debugging of RCU internals.)
In addition, if one of the RCU flavor's grace period has stalled, this
will invoke rcu_momentary_dyntick_idle(), resulting in a heavy-weight
quiescent state visible from other CPUs.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Merge commit from Sasha Levin fixing a bug where __this_cpu()
  was used in preemptible code. ]
2015-01-15 23:33:14 -08:00
Paul E. McKenney
6ccd2ecd42 rcu: Improve diagnostics for spurious RCU CPU stall warnings
The current RCU CPU stall warning code will print "Stall ended before
state dump start" any time that the stall-warning code is triggered on
a CPU that has already reported a quiescent state for the current grace
period and if all quiescent states have been reported for the current
grace period.  However, a true stall can result in these symptoms, for
example, by preventing RCU's grace-period kthreads from ever running

This commit therefore checks for this condition, reporting the end of
the stall only if one of the grace-period counters has actually advanced.
Otherwise, it reports the last time that the grace-period kthread made
meaningful progress.  (In normal situations, the grace-period kthread
should make meaningful progress at least every jiffies_till_next_fqs
jiffies.)

Reported-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Miroslav Benes <mbenes@suse.cz>
2015-01-06 11:05:27 -08:00
Xie XiuQi
84596ccbf1 documentation: Update sysfs path for rcu_cpu_stall_timeout
Commit 6bfc09e232 ("rcu: Provide RCU CPU stall warnings for tiny RCU")
moved the rcu_cpu_stall_timeout module parameter from rcutree.c to
rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This
commit therefore repairs this omission.

commit 96224daa16 ("documentation: Update sysfs path for rcu_cpu_stall_suppress")
updated the path for rcu_cpu_stall_suppress, but failed to update for
rcu_cpu_stall_timeout.

Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-06 10:57:24 -08:00
Paul E. McKenney
9ea6c58856 Merge branches 'torture.2014.11.03a', 'cpu.2014.11.03a', 'doc.2014.11.13a', 'fixes.2014.11.13a', 'signal.2014.10.29a' and 'rt.2014.10.29a' into HEAD
cpu.2014.11.03a: Changes for per-CPU variables.
doc.2014.11.13a: Documentation updates.
fixes.2014.11.13a: Miscellaneous fixes.
signal.2014.10.29a: Signal changes.
rt.2014.10.29a: Real-time changes.
torture.2014.11.03a: torture-test changes.
2014-11-13 10:39:04 -08:00
Pranith Kumar
28f6569ab7 rcu: Remove redundant TREE_PREEMPT_RCU config option
PREEMPT_RCU and TREE_PREEMPT_RCU serve the same function after
TINY_PREEMPT_RCU has been removed. This patch removes TREE_PREEMPT_RCU
and uses PREEMPT_RCU config option in its place.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-10-29 10:20:05 -07:00
Paul E. McKenney
0eafa46823 rcu: Remove CONFIG_RCU_CPU_STALL_VERBOSE
The CONFIG_RCU_CPU_STALL_VERBOSE Kconfig parameter causes preemptible
RCU's CPU stall warnings to dump out any preempted tasks that are blocking
the current RCU grace period.  This information is useful, and the default
has been CONFIG_RCU_CPU_STALL_VERBOSE=y for some years.  It is therefore
time for this commit to remove this Kconfig parameter, so that future
kernel builds will always act as if CONFIG_RCU_CPU_STALL_VERBOSE=y.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-10-28 13:48:13 -07:00
Paul E. McKenney
37fe5f0e27 documentation: Add verbiage on RCU-tasks stall warning messages
This commit documents RCU-tasks stall warning messages and also describes
when to use the new cond_resched_rcu_qs() API.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-09-07 16:27:28 -07:00
Ken Helias
1d023284c3 list: fix order of arguments for hlist_add_after(_rcu)
All other add functions for lists have the new item as first argument
and the position where it is added as second argument.  This was changed
for no good reason in this function and makes using it unnecessary
confusing.

The name was changed to hlist_add_behind() to cause unconverted code to
generate a compile error instead of using the wrong parameter order.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Ken Helias <kenhelias@firemail.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>	[intel driver bits]
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-08-06 18:01:24 -07:00
Paul E. McKenney
9963185c04 documentation: Add pointer to percpu-ref for RCU and refcount
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2014-07-08 08:32:56 -07:00
Pranith Kumar
5e40ad7f6a documentation: Update reference, kerneltrap.org no longer works
The kerneltrap.org site no longer works, so this commit updates it to
a working reference, namely gmane.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-07-08 08:14:09 -07:00
Paul E. McKenney
d07e6d080d documentation: Update API documentation
This commit updates the list of RCU API members in whatisRCU.txt.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29 08:38:53 -07:00
Paul E. McKenney
b4c5bf3534 documentation: Record rcu_dereference() value mishandling
Recent LKML discussings (see http://lwn.net/Articles/586838/ and
http://lwn.net/Articles/588300/ for the LWN writeups) brought out
some ways of misusing the return value from rcu_dereference() that
are not necessarily completely intuitive.  This commit therefore
documents what can and cannot safely be done with these values.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29 08:38:33 -07:00
Paul E. McKenney
96224daa16 documentation: Update sysfs path for rcu_cpu_stall_suppress
Commit 6bfc09e232 (rcu: Provide RCU CPU stall warnings for tiny RCU)
moved the rcu_cpu_stall_suppress module parameter from rcutree.c to
rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt.  This
commit therefore repairs this omission.

Reported-by: Kirill Tkhai <tkhai@yandex.ru>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29 08:21:50 -07:00
Paul E. McKenney
e4696a1d3b documentation: Fix some inconsistencies in RTFP.txt
Some of the early history leaves out some citations and vice versa.  This
commit fixes these up.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-02-17 14:56:10 -08:00
Paul E. McKenney
6e67669678 documentation: Document call_rcu() safety mechanisms and limitations
The call_rcu() family of primitives will take action to accelerate
grace periods when the number of callbacks pending on a given CPU
becomes excessive.  Although this safety mechanism can be useful,
it is no substitute for users of call_rcu() having rate-limit controls
in place.  This commit adds this nuance to the documentation.

Reported-by: "Michael S. Tsirkin" <mst@redhat.com>
Reported-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-02-17 14:55:58 -08:00
Henrik Austad
3cf8ca1c25 Documentation/: update 00-INDEX files
Some of the 00-INDEX files are somewhat outdated and some folders does
not contain 00-INDEX at all.  Only outdated (with the notably exception
of spi) indexes are touched here, the 169 folders without 00-INDEX has
not been touched.

New 00-INDEX
 - spi/* was added in a series of commits dating back to 2006

Added files (missing in (*/)00-INDEX)
 - dmatest.txt was added by commit 851b7e16a0 ("dmatest: run test via
   debugfs")
 - this_cpu_ops.txt was added by commit a1b2a555d6 ("percpu: add
   documentation on this_cpu operations")
 - ww-mutex-design.txt was added by commit 040a0a3710 ("mutex: Add
   support for wound/wait style locks")
 - bcache.txt was added by commit cafe563591 ("bcache: A block layer
   cache")
 - kernel-per-CPU-kthreads.txt was added by commit 49717cb404
   ("kthread: Document ways of reducing OS jitter due to per-CPU
   kthreads")
 - phy.txt was added by commit ff76496347 ("drivers: phy: add generic
   PHY framework")
 - block/null_blk was added by commit 12f8f4fc03 ("null_blk:
   documentation")
 - module-signing.txt was added by commit 3cafea3076 ("Add
   Documentation/module-signing.txt file")
 - assoc_array.txt was added by commit 3cb989501c ("Add a generic
   associative array implementation.")
 - arm/IXP4xx was part of the initial repo
 - arm/cluster-pm-race-avoidance.txt was added by commit 7fe31d28e8
   ("ARM: mcpm: introduce helpers for platform coherency exit/setup")
 - arm/firmware.txt was added by commit 7366b92a77 ("ARM: Add
   interface for registering and calling firmware-specific operations")
 - arm/kernel_mode_neon.txt was added by commit 2afd0a0524 ("ARM:
   7825/1: document the use of NEON in kernel mode")
 - arm/tcm.txt was added by commit bc581770cf ("ARM: 5580/2: ARM TCM
   (Tightly-Coupled Memory) support v3")
 - arm/vlocks.txt was added by commit 9762f12d3e ("ARM: mcpm: Add
   baremetal voting mutexes")
 - blackfin/gptimers-example.c, Makefile was added by commit
   4b60779d5e ("Blackfin: add an example showing how to use the
   gptimers API")
 - devicetree/usage-model.txt was added by commit 31134efc68 ("dt:
   Linux DT usage model documentation")
 - fb/api.txt was added by commit fb21c2f428 ("fbdev: Add FOURCC-based
   format configuration API")
 - fb/sm501.txt was added by commit e6a0498071 ("video, sm501: add
   edid and commandline support")
 - fb/udlfb.txt was added by commit 96f8d864af ("fbdev: move udlfb out
   of staging.")
 - filesystems/Makefile was added by commit 1e0051ae48
   ("Documentation/fs/: split txt and source files")
 - filesystems/nfs/nfsd-admin-interfaces.txt was added by commit
   8a4c6e19cf ("nfsd: document kernel interfaces for nfsd
   configuration")
 - ide/warm-plug-howto.txt was added by commit f74c91413e ("ide: add
   warm-plug support for IDE devices (take 2)")
 - laptops/Makefile was added by commit d49129accc
   ("Documentation/laptop/: split txt and source files")
 - leds/leds-blinkm.txt was added by commit b54cf35a7f ("LEDS: add
   BlinkM RGB LED driver, documentation and update MAINTAINERS")
 - leds/ledtrig-oneshot.txt was added by commit 5e417281cd ("leds: add
   oneshot trigger")
 - leds/ledtrig-transient.txt was added by commit 44e1e9f8e7 ("leds:
   add new transient trigger for one shot timer activation")
 - m68k/README.buddha was part of the initial repo
 - networking/LICENSE.(qla3xxx|qlcnic|qlge) was added by commits
   40839129f7, c4e84bde1d, 5a4faa8737
 - networking/Makefile was added by commit 3794f3e812 ("docsrc: build
   Documentation/ sources")
 - networking/i40evf.txt was added by commit 105bf2fe6b ("i40evf: add
   driver to kernel build system")
 - networking/ipsec.txt was added by commit b3c6efbc36 ("xfrm: Add
   file to document IPsec corner case")
 - networking/mac80211-auth-assoc-deauth.txt was added by commit
   3cd7920a2b ("mac80211: add auth/assoc/deauth flow diagram")
 - networking/netlink_mmap.txt was added by commit 5683264c39
   ("netlink: add documentation for memory mapped I/O")
 - networking/nf_conntrack-sysctl.txt was added by commit c9f9e0e159
   ("netfilter: doc: add nf_conntrack sysctl api documentation") lan)
 - networking/team.txt was added by commit 3d249d4ca7 ("net: introduce
   ethernet teaming device")
 - networking/vxlan.txt was added by commit d342894c5d ("vxlan:
   virtual extensible lan")
 - power/runtime_pm.txt was added by commit 5e928f77a0 ("PM: Introduce
   core framework for run-time PM of I/O devices (rev.  17)")
 - power/charger-manager.txt was added by commit 3bb3dbbd56
   ("power_supply: Add initial Charger-Manager driver")
 - RCU/lockdep-splat.txt was added by commit d7bd2d68aa ("rcu:
   Document interpretation of RCU-lockdep splats")
 - s390/kvm.txt was added by 5ecee4b (KVM: s390: API documentation)
 - s390/qeth.txt was added by commit b4d72c08b3 ("qeth: bridgeport
   support - basic control")
 - scheduler/sched-bwc.txt was added by commit 88ebc08ea9 ("sched: Add
   documentation for bandwidth control")
 - scsi/advansys.txt was added by commit 4bd6d7f356 ("[SCSI] advansys:
   Move documentation to Documentation/scsi")
 - scsi/bfa.txt was added by commit 1ec90174bd ("[SCSI] bfa: add
   readme file")
 - scsi/bnx2fc.txt was added by commit 12b8fc10ea ("[SCSI] bnx2fc: Add
   driver documentation")
 - scsi/cxgb3i.txt was added by commit c3673464eb ("[SCSI] cxgb3i: Add
   cxgb3i iSCSI driver.")
 - scsi/hpsa.txt was added by commit 992ebcf14f ("[SCSI] hpsa: Add
   hpsa.txt to Documentation/scsi")
 - scsi/link_power_management_policy.txt was added by commit
   ca77329fb7 ("[libata] Link power management infrastructure")
 - scsi/osd.txt was added by commit 78e0c621de ("[SCSI] osd:
   Documentation for OSD library")
 - scsi/scsi-parameter.txt was created/moved by commit 163475fb11
   ("Documentation: move SCSI parameters to their own text file")
 - serial/driver was part of the initial repo
 - serial/n_gsm.txt was added by commit 323e84122e ("n_gsm: add a
   documentation")
 - timers/Makefile was added by commit 3794f3e812 ("docsrc: build
   Documentation/ sources")
 - virt/kvm/s390.txt was added by commit d9101fca3d ("KVM: s390:
   diagnose call documentation")
 - vm/split_page_table_lock was added by commit 49076ec2cc ("mm:
   dynamically allocate page->ptl if it cannot be embedded to struct
   page")
 - w1/slaves/w1_ds28e04 was added by commit fbf7f7b4e2 ("w1: Add
   1-wire slave device driver for DS28E04-100")
 - w1/masters/omap-hdq was added by commit e0a29382c6 ("hdq:
   documentation for OMAP HDQ")
 - x86/early-microcode.txt was added by commit 0d91ea86a8 ("x86, doc:
   Documentation for early microcode loading")
 - x86/earlyprintk.txt was added by commit a1aade4788 ("x86/doc:
   mini-howto for using earlyprintk=dbgp")
 - x86/entry_64.txt was added by commit 8b4777a4b5 ("x86-64: Document
   some of entry_64.S")
 - x86/pat.txt was added by commit d27554d874 ("x86: PAT
   documentation")

Moved files
 - arm/kernel_user_helpers.txt was moved out of arch/arm/kernel by
   commit 37b8304642 ("ARM: kuser: move interface documentation out of
   the source code")
 - efi-stub.txt was moved out of x86/ and down into Documentation/ in
   commit 4172fe2f8a ("EFI stub documentation updates")
 - laptops/hpfall.c was moved out of hwmon/ and into laptops/ in commit
   efcfed9bad ("Move hp_accel to drivers/platform/x86")
 - commit 5616c23ad9 ("x86: doc: move x86-generic documentation from
   Doc/x86/i386"):
   * x86/usb-legacy-support.txt
   * x86/boot.txt
   * x86/zero_page.txt
 - power/video_extension.txt was moved to acpi in commit 70e66e4df1
   ("ACPI / video: move video_extension.txt to Documentation/acpi")

Removed files (left in 00-INDEX)
 - memory.txt was removed by commit 00ea8990aa ("memory.txt: remove
   stray information")
 - gpio.txt was moved to gpio/ in commit fd8e198cfc ("Documentation:
   gpiolib: document new interface")
 - networking/DLINK.txt was removed by commit 168e06ae26
   ("drivers/net: delete old parallel port de600/de620 drivers")
 - serial/hayes-esp.txt was removed by commit f53a2ade0b ("tty: esp:
   remove broken driver")
 - s390/TAPE was removed by commit 9e280f6693 ("[S390] remove tape
   block docu")
 - vm/locking was removed by commit 57ea8171d2 ("mm: documentation:
   remove hopelessly out-of-date locking doc")
 - laptops/acer-wmi.txt was remvoed by commit 020036678e ("acer-wmi:
   Delete out-of-date documentation")

Typos/misc issues
 - rpc-server-gss.txt was added as knfsd-rpcgss.txt in commit
   030d794bf4 ("SUNRPC: Use gssproxy upcall for server RPCGSS
   authentication.")
 - commit b88cf73d92 ("net: add missing entries to
   Documentation/networking/00-INDEX")
   * generic-hdlc.txt was added as generic_hdlc.txt
   * spider_net.txt was added as spider-net.txt
 - w1/master/mxc-w1 was added as mxc_w1 by commit a5fd9139f7 ("w1: add
   1-wire master driver for i.MX27 / i.MX31")
 - s390/zfcpdump.txt was added as zfcpdump by commit 6920c12a40
   ("[S390] Add Documentation/s390/00-INDEX.")

Signed-off-by: Henrik Austad <henrik@austad.us>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>	[rcu bits]
Acked-by: Rob Landley <rob@landley.net>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Mark Brown <broonie@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Len Brown <len.brown@intel.com>
Cc: James Bottomley <JBottomley@parallels.com>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-02-10 16:01:40 -08:00
Paul E. McKenney
0d3c55bc9f Merge branches 'doc.2013.12.03a', 'fixes.2013.12.12a', 'rcutorture.2013.12.03a' and 'sparse.2013.12.12a' into HEAD
doc.2013.12.03a: Topic branch for documentation changes.
fixes.2013.12.12a: Topic branch for miscellaneous fixes.
rcutorture.2013.12.03a: Topic branch for new rcutorture/KVM scripting.
sparse.2013.12.12a: Topic branch for sparse-RCU changes.
2013-12-12 12:35:38 -08:00
Paul E. McKenney
96d3fd0d31 rcu: Break call_rcu() deadlock involving scheduler and perf
Dave Jones got the following lockdep splat:

>  ======================================================
>  [ INFO: possible circular locking dependency detected ]
>  3.12.0-rc3+ #92 Not tainted
>  -------------------------------------------------------
>  trinity-child2/15191 is trying to acquire lock:
>   (&rdp->nocb_wq){......}, at: [<ffffffff8108ff43>] __wake_up+0x23/0x50
>
> but task is already holding lock:
>   (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #3 (&ctx->lock){-.-...}:
>         [<ffffffff810cc243>] lock_acquire+0x93/0x200
>         [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80
>         [<ffffffff811500ff>] __perf_event_task_sched_out+0x2df/0x5e0
>         [<ffffffff81091b83>] perf_event_task_sched_out+0x93/0xa0
>         [<ffffffff81732052>] __schedule+0x1d2/0xa20
>         [<ffffffff81732f30>] preempt_schedule_irq+0x50/0xb0
>         [<ffffffff817352b6>] retint_kernel+0x26/0x30
>         [<ffffffff813eed04>] tty_flip_buffer_push+0x34/0x50
>         [<ffffffff813f0504>] pty_write+0x54/0x60
>         [<ffffffff813e900d>] n_tty_write+0x32d/0x4e0
>         [<ffffffff813e5838>] tty_write+0x158/0x2d0
>         [<ffffffff811c4850>] vfs_write+0xc0/0x1f0
>         [<ffffffff811c52cc>] SyS_write+0x4c/0xa0
>         [<ffffffff8173d4e4>] tracesys+0xdd/0xe2
>
> -> #2 (&rq->lock){-.-.-.}:
>         [<ffffffff810cc243>] lock_acquire+0x93/0x200
>         [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80
>         [<ffffffff810980b2>] wake_up_new_task+0xc2/0x2e0
>         [<ffffffff81054336>] do_fork+0x126/0x460
>         [<ffffffff81054696>] kernel_thread+0x26/0x30
>         [<ffffffff8171ff93>] rest_init+0x23/0x140
>         [<ffffffff81ee1e4b>] start_kernel+0x3f6/0x403
>         [<ffffffff81ee1571>] x86_64_start_reservations+0x2a/0x2c
>         [<ffffffff81ee1664>] x86_64_start_kernel+0xf1/0xf4
>
> -> #1 (&p->pi_lock){-.-.-.}:
>         [<ffffffff810cc243>] lock_acquire+0x93/0x200
>         [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
>         [<ffffffff810979d1>] try_to_wake_up+0x31/0x350
>         [<ffffffff81097d62>] default_wake_function+0x12/0x20
>         [<ffffffff81084af8>] autoremove_wake_function+0x18/0x40
>         [<ffffffff8108ea38>] __wake_up_common+0x58/0x90
>         [<ffffffff8108ff59>] __wake_up+0x39/0x50
>         [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
>         [<ffffffff81111450>] __call_rcu+0x140/0x820
>         [<ffffffff81111b8d>] call_rcu+0x1d/0x20
>         [<ffffffff81093697>] cpu_attach_domain+0x287/0x360
>         [<ffffffff81099d7e>] build_sched_domains+0xe5e/0x10a0
>         [<ffffffff81efa7fc>] sched_init_smp+0x3b7/0x47a
>         [<ffffffff81ee1f4e>] kernel_init_freeable+0xf6/0x202
>         [<ffffffff817200be>] kernel_init+0xe/0x190
>         [<ffffffff8173d22c>] ret_from_fork+0x7c/0xb0
>
> -> #0 (&rdp->nocb_wq){......}:
>         [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0
>         [<ffffffff810cc243>] lock_acquire+0x93/0x200
>         [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
>         [<ffffffff8108ff43>] __wake_up+0x23/0x50
>         [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
>         [<ffffffff81111450>] __call_rcu+0x140/0x820
>         [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30
>         [<ffffffff81149abf>] put_ctx+0x4f/0x70
>         [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230
>         [<ffffffff81056b8d>] do_exit+0x30d/0xcc0
>         [<ffffffff8105893c>] do_group_exit+0x4c/0xc0
>         [<ffffffff810589c4>] SyS_exit_group+0x14/0x20
>         [<ffffffff8173d4e4>] tracesys+0xdd/0xe2
>
> other info that might help us debug this:
>
> Chain exists of:
>   &rdp->nocb_wq --> &rq->lock --> &ctx->lock
>
>   Possible unsafe locking scenario:
>
>         CPU0                    CPU1
>         ----                    ----
>    lock(&ctx->lock);
>                                 lock(&rq->lock);
>                                 lock(&ctx->lock);
>    lock(&rdp->nocb_wq);
>
>  *** DEADLOCK ***
>
> 1 lock held by trinity-child2/15191:
>  #0:  (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230
>
> stack backtrace:
> CPU: 2 PID: 15191 Comm: trinity-child2 Not tainted 3.12.0-rc3+ #92
>  ffffffff82565b70 ffff880070c2dbf8 ffffffff8172a363 ffffffff824edf40
>  ffff880070c2dc38 ffffffff81726741 ffff880070c2dc90 ffff88022383b1c0
>  ffff88022383aac0 0000000000000000 ffff88022383b188 ffff88022383b1c0
> Call Trace:
>  [<ffffffff8172a363>] dump_stack+0x4e/0x82
>  [<ffffffff81726741>] print_circular_bug+0x200/0x20f
>  [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0
>  [<ffffffff810c6439>] ? get_lock_stats+0x19/0x60
>  [<ffffffff8100b2f4>] ? native_sched_clock+0x24/0x80
>  [<ffffffff810cc243>] lock_acquire+0x93/0x200
>  [<ffffffff8108ff43>] ? __wake_up+0x23/0x50
>  [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
>  [<ffffffff8108ff43>] ? __wake_up+0x23/0x50
>  [<ffffffff8108ff43>] __wake_up+0x23/0x50
>  [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
>  [<ffffffff81111450>] __call_rcu+0x140/0x820
>  [<ffffffff8109bc8f>] ? local_clock+0x3f/0x50
>  [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30
>  [<ffffffff81149abf>] put_ctx+0x4f/0x70
>  [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230
>  [<ffffffff81056b8d>] do_exit+0x30d/0xcc0
>  [<ffffffff810c9af5>] ? trace_hardirqs_on_caller+0x115/0x1e0
>  [<ffffffff810c9bcd>] ? trace_hardirqs_on+0xd/0x10
>  [<ffffffff8105893c>] do_group_exit+0x4c/0xc0
>  [<ffffffff810589c4>] SyS_exit_group+0x14/0x20
>  [<ffffffff8173d4e4>] tracesys+0xdd/0xe2

The underlying problem is that perf is invoking call_rcu() with the
scheduler locks held, but in NOCB mode, call_rcu() will with high
probability invoke the scheduler -- which just might want to use its
locks.  The reason that call_rcu() needs to invoke the scheduler is
to wake up the corresponding rcuo callback-offload kthread, which
does the job of starting up a grace period and invoking the callbacks
afterwards.

One solution (championed on a related problem by Lai Jiangshan) is to
simply defer the wakeup to some point where scheduler locks are no longer
held.  Since we don't want to unnecessarily incur the cost of such
deferral, the task before us is threefold:

1.	Determine when it is likely that a relevant scheduler lock is held.

2.	Defer the wakeup in such cases.

3.	Ensure that all deferred wakeups eventually happen, preferably
	sooner rather than later.

We use irqs_disabled_flags() as a proxy for relevant scheduler locks
being held.  This works because the relevant locks are always acquired
with interrupts disabled.  We may defer more often than needed, but that
is at least safe.

The wakeup deferral is tracked via a new field in the per-CPU and
per-RCU-flavor rcu_data structure, namely ->nocb_defer_wakeup.

This flag is checked by the RCU core processing.  The __rcu_pending()
function now checks this flag, which causes rcu_check_callbacks()
to initiate RCU core processing at each scheduling-clock interrupt
where this flag is set.  Of course this is not sufficient because
scheduling-clock interrupts are often turned off (the things we used to
be able to count on!).  So the flags are also checked on entry to any
state that RCU considers to be idle, which includes both NO_HZ_IDLE idle
state and NO_HZ_FULL user-mode-execution state.

This approach should allow call_rcu() to be invoked regardless of what
locks you might be holding, the key word being "should".

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
2013-12-03 10:10:18 -08:00
Paul E. McKenney
c9592ecb98 rcu: Fix typo in Documentation/RCU/trace.txt
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-12-03 10:08:56 -08:00
Michael Opdenacker
4b0d3f0fde rcu: Fix occurrence of "the the" in checklist.txt
Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add "then" as suggested by Josh Triplett. ]
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-09-25 10:07:02 -07:00
Paul E. McKenney
64d3b7a1d5 rcu: Update stall-warning documentation
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-09-25 06:49:37 -07:00
Paul E. McKenney
25f27ce4a6 Merge branches 'doc.2013.08.19a', 'fixes.2013.08.20a', 'sysidle.2013.08.31a' and 'torture.2013.08.20a' into HEAD
doc.2013.08.19a: Documentation updates
fixes.2013.08.20a: Miscellaneous fixes
sysidle.2013.08.31a: Detect system-wide idle state.
torture.2013.08.20a: rcutorture updates.
2013-08-31 14:44:45 -07:00
Paul E. McKenney
2ec1f2d987 rcu: Increase rcutorture test coverage
Currently, rcutorture has separate torture_types to test synchronous,
asynchronous, and expedited grace-period primitives.  This has
two disadvantages: (1) Three times the number of runs to cover the
combinations and (2) Little testing of concurrent combinations of the
three options.  This commit therefore adds a pair of module parameters
that control normal and expedited state, with the default being both
types, randomly selected, by the fakewriter processes, thus reducing
source-code size and increasing test coverage.  In addtion, the writer
task switches between asynchronous-normal and expedited grace-period
primitives driven by the same pair of module parameters.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-20 11:38:41 -07:00
Paul E. McKenney
6ae3771850 rcu: Update RTFP documentation
Note that this commit also updates the formatting of serveral of the
bibtex entries to conform to that of my .bib files.  I started
accumulating entries back in the 1980s, back when bibtex insisted
that comma (",") was a separator, not a terminator.  This rule forced
commas to the fronts of lines.  25 years later, bibtex allows commas
to be terminators, but I am too lazy to rework all my .bib files.
Keeping the same format as my .bib files allows my to simply
incorporate my RCU.bib file into Documentation/RCU/RTFP.txt, which
is much easier than my earlier practice of keeping track of what
had changed and adding individual entries.  (I sometimes find relevant
papers that were published some years back, for example.)

In addition, this change adds entries for papers published in the
last year or so.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-19 21:39:27 -07:00
Paul E. McKenney
d84297c99b rcu: Fix rcu_barrier() documentation
There was a time when rcu_barrier() was guaranteed to wait for at least
a grace period, but that time ended due to energy-efficiency concerns.
So now rcu_barrier() is a no-op if there are no RCU callbacks queued in
the system.  This commit updates the documentation to reflect this change.

Now, rcu_barrier() often does wait for a grace period, so, one could
imagine some modification to rcu_barrier() to more efficiently handle
cases where both rcu_barrier() and a grace period are needed.  But this
must wait until someone shows a real-world need for a change.

Reported-by: Bob Copeland <bob@cozybit.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18 17:05:32 -07:00
Paul E. McKenney
be77f87c00 Merge branches 'cbnum.2013.06.10a', 'doc.2013.06.10a', 'fixes.2013.06.10a', 'srcu.2013.06.10a' and 'tiny.2013.06.10a' into HEAD
cbnum.2013.06.10a: Apply simplifications stemming from the new callback
	numbering.

doc.2013.06.10a: Documentation updates.

fixes.2013.06.10a: Miscellaneous fixes.

srcu.2013.06.10a: Updates to SRCU.

tiny.2013.06.10a: Eliminate TINY_PREEMPT_RCU.
2013-06-10 13:46:44 -07:00
Paul E. McKenney
7807acdb6b rcu: Remove TINY_PREEMPT_RCU tracing documentation
Because TINY_PREEMPT_RCU is no more, this commit removes its tracing
formats from the documentation.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10 13:45:52 -07:00
Paul E. McKenney
99f88919f8 rcu: Remove srcu_read_lock_raw() and srcu_read_unlock_raw().
These interfaces never did get used, so this commit removes them,
their rcutorture tests, and documentation referencing them.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10 13:45:25 -07:00
Frederic Weisbecker
c032862fba Merge commit '8700c95adb03' into timers/nohz
The full dynticks tree needs the latest RCU and sched
upstream updates in order to fix some dependencies.

Merge a common upstream merge point that has these
updates.

Conflicts:
	include/linux/perf_event.h
	kernel/rcutree.h
	kernel/rcutree_plugin.h

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2013-05-02 17:54:19 +02:00
Frederic Weisbecker
3451d0243c nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMON
We are planning to convert the dynticks Kconfig options layout
into a choice menu. The user must be able to easily pick
any of the following implementations: constant periodic tick,
idle dynticks, full dynticks.

As this implies a mutual exclusion, the two dynticks implementions
need to converge on the selection of a common Kconfig option in order
to ease the sharing of a common infrastructure.

It would thus seem pretty natural to reuse CONFIG_NO_HZ to
that end. It already implements all the idle dynticks code
and the full dynticks depends on all that code for now.
So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.

On the other hand we want to stay backward compatible: if
CONFIG_NO_HZ is set in an older config file, we want to
enable CONFIG_NO_HZ_IDLE by default.

But we can't afford both at the same time or we run into
a circular dependency:

1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
   CONFIG_NO_HZ
2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE

We might be able to support that from Kconfig/Kbuild but it
may not be wise to introduce such a confusing behaviour.

So to solve this, create a new CONFIG_NO_HZ_COMMON option
which gathers the common code between idle and full dynticks
(that common code for now is simply the idle dynticks code)
and select it from their referring Kconfig.

Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
to it for backward compatibility.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
2013-04-03 13:56:03 +02:00
Paul E. McKenney
6d87669357 Merge branches 'doc.2013.03.12a', 'fixes.2013.03.13a' and 'idlenocb.2013.03.26b' into HEAD
doc.2013.03.12a: Documentation changes.

fixes.2013.03.13a: Miscellaneous fixes.

idlenocb.2013.03.26b: Remove restrictions on no-CBs CPUs, make
	RCU_FAST_NO_HZ take advantage of numbered callbacks, add
	callback acceleration based on numbered callbacks.
2013-03-26 08:07:38 -07:00
Paul E. McKenney
6231069bda rcu: Add softirq-stall indications to stall-warning messages
If RCU's softirq handler is prevented from executing, an RCU CPU stall
warning can result.  Ways to prevent RCU's softirq handler from executing
include: (1) CPU spinning with interrupts disabled, (2) infinite loop
in some softirq handler, and (3) in -rt kernels, an infinite loop in a
set of real-time threads running at priorities higher than that of RCU's
softirq handler.

Because this situation can be difficult to track down, this commit causes
the count of RCU softirq handler invocations to be printed with RCU
CPU stall warnings.  This information does require some interpretation,
as now documented in Documentation/RCU/stallwarn.txt.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>
2013-03-13 14:43:56 -07:00
Paul E. McKenney
3f944adb9d rcu: Documentation update
This commit applies a few updates based on a quick review of the RCU
documentations.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-03-12 14:09:02 -07:00
Paul E. McKenney
4357fb570b rcu: Make bugginess of code sample more evident
One of the code samples in whatisRCU.txt shows a bug, but someone scanning
the document quickly might mistake it for a valid use of RCU.  Add some
screaming comments to help keep speed-readers on track.

Reported-by: Nathan Zimmer <nzimmer@sgi.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2013-03-12 14:09:01 -07:00
Paul E. McKenney
aac1cda34b Merge branches 'urgent.2012.10.27a', 'doc.2012.11.16a', 'fixes.2012.11.13a', 'srcu.2012.10.27a', 'stall.2012.11.13a', 'tracing.2012.11.08a' and 'idle.2012.10.24a' into HEAD
urgent.2012.10.27a: Fix for RCU user-mode transition (already in -tip).

doc.2012.11.08a: Documentation updates, most notably codifying the
	memory-barrier guarantees inherent to grace periods.

fixes.2012.11.13a: Miscellaneous fixes.

srcu.2012.10.27a: Allow statically allocated and initialized srcu_struct
	structures (courtesy of Lai Jiangshan).

stall.2012.11.13a: Add more diagnostic information to RCU CPU stall
	warnings, also decrease from 60 seconds to 21 seconds.

hotplug.2012.11.08a: Minor updates to CPU hotplug handling.

tracing.2012.11.08a: Improved debugfs tracing, courtesy of Michael Wang.

idle.2012.10.24a: Updates to RCU idle/adaptive-idle handling, including
	a boot parameter that maps normal grace periods to expedited.

Resolved conflict in kernel/rcutree.c due to side-by-side change.
2012-11-16 09:59:58 -08:00
Paul E. McKenney
d484a21513 rcu: Add documentation for the new rcuexp debugfs trace file
This commit adds the documentation of the rcuexp debugfs trace file
that records statistics for expedited grace periods.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-11-16 09:55:31 -08:00
Paul E. McKenney
40e80c469f rcu: Update documentation for TREE_RCU debugfs tracing
This commit updates the tracing documentation to reflect the new
format that has per-RCU-flavor directories.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-11-16 09:54:02 -08:00
Paul E. McKenney
bb08f76d84 rcu: Remove list_for_each_continue_rcu()
The list_for_each_continue_rcu() macro is no longer used, so this commit
removes it.  The list_for_each_entry_continue_rcu() macro should be
used instead.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-11-13 14:08:21 -08:00
Paul E. McKenney
a4d611fdca rcu: Document alternative RCU/reference-count algorithms
The approach for mixing RCU and reference counting listed in the RCU
documentation only describes one possible approach.  This approach can
result in failure on the read side, which is nice if you want fresh data,
but not so good if you want simple code.  This commit therefore adds
two additional approaches that feature unconditional reference-count
acquisition by RCU readers.  These approaches are very similar to that
used in the security code.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-11-08 11:44:38 -08:00
Kees Cook
57d34a6cee rcu: Update docs to include kfree_rcu()
Mention kfree_rcu() in the call_rcu() section.  Additionally fix the
example code for list replacement that used the wrong structure element.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-11-08 11:44:25 -08:00
Dhaval Giani
0f9574d832 rcu: Correct the name of a reference in list of RCU papers
Trying to go through the history of RCU (not for the weak
minded) led me to search for a non-existent paper.

Correct it to the actual reference

Signed-off-by: Dhaval Giani <dhaval.giani@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-10-23 14:44:47 -07:00
Paul E. McKenney
bda4ec9f6a Merge branches 'bigrt.2012.09.23a', 'doctorture.2012.09.23a', 'fixes.2012.09.23a', 'hotplug.2012.09.23a' and 'idlechop.2012.09.23a' into HEAD
bigrt.2012.09.23a contains additional commits to reduce scheduling latency
	from RCU on huge systems (many hundrends or thousands of CPUs).

doctorture.2012.09.23a contains documentation changes and rcutorture fixes.

fixes.2012.09.23a contains miscellaneous fixes.

hotplug.2012.09.23a contains CPU-hotplug-related changes.

idle.2012.09.23a fixes architectures for which RCU no longer considered
	the idle loop to be a quiescent state due to earlier
	adaptive-dynticks changes.  Affected architectures are alpha,
	cris, frv, h8300, m32r, m68k, mn10300, parisc, score, xtensa,
	and ia64.
2012-09-24 20:02:22 -07:00
Paul E. McKenney
86f343b50b rcu: Fix CONFIG_RCU_FAST_NO_HZ stall warning message
The print_cpu_stall_fast_no_hz() function attempts to print -1 when
the ->idle_gp_timer is not pending, but unsigned arithmetic causes it
to instead print ULONG_MAX, which is 4294967295 on 32-bit systems and
18446744073709551615 on 64-bit systems.  Neither of these are the most
reader-friendly values, so this commit instead causes "timer not pending"
to be printed when ->idle_gp_timer is not pending.

Reported-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-09-23 07:42:52 -07:00
Paul E. McKenney
2aef619c75 rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits
The current documentation did not help someone grepping for SRCU to
learn that disabling preemption is not a replacement for srcu_read_lock(),
so upgrade the documentation to bring this out, not just for SRCU,
but also for RCU-bh.  Also document the fact that SRCU readers are
respected on CPUs executing in user mode, idle CPUs, and even on
offline CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2012-09-23 07:42:23 -07:00
Paul E. McKenney
4605c0143c rcu: Adjust debugfs tracing for kthread-based quiescent-state forcing
Moving quiescent-state forcing into a kthread dispenses with the need
for the ->n_rp_need_fqs field, so this commit removes it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2012-09-23 07:41:54 -07:00
Paul E. McKenney
74d874e7bd rcu: Update documentation to cover call_srcu() and srcu_barrier().
The advent of call_srcu() and srcu_barrier() obsoleted some of the
documentation, so this commit brings that up to date.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-07-02 12:34:03 -07:00
Paul E. McKenney
fae4b54f28 rcu: Introduce rcutorture testing for rcu_barrier()
Although rcutorture does invoke rcu_barrier() and friends, it cannot
really be called a torture test given that it invokes them only once
at the end of the test.  This commit therefore introduces heavy-duty
rcutorture testing for rcu_barrier(), which may be carried out
concurrently with normal rcutorture testing.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-04-30 10:48:18 -07:00
Paul E. McKenney
236fefafe5 rcu: Call out dangers of expedited RCU primitives
The expedited RCU primitives can be quite useful, but they have some
high costs as well.  This commit updates and creates docbook comments
calling out the costs, and updates the RCU documentation as well.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:06:08 -08:00
Paul E. McKenney
2036d94a7b rcu: Rework detection of use of RCU by offline CPUs
Because newly offlined CPUs continue executing after completing the
CPU_DYING notifiers, they legitimately enter the scheduler and use
RCU while appearing to be offline.  This calls for a more sophisticated
approach as follows:

1.	RCU marks the CPU online during the CPU_UP_PREPARE phase.

2.	RCU marks the CPU offline during the CPU_DEAD phase.

3.	Diagnostics regarding use of read-side RCU by offline CPUs use
	RCU's accounting rather than the cpu_online_map.  (Note that
	__call_rcu() still uses cpu_online_map to detect illegal
	invocations within CPU_DYING notifiers.)

4.	Offline CPUs are prevented from hanging the system by
	force_quiescent_state(), which pays attention to cpu_online_map.
	Some additional work (in a later commit) will be needed to
	guarantee that force_quiescent_state() waits a full jiffy before
	assuming that a CPU is offline, for example, when called from
	idle entry.  (This commit also makes the one-jiffy wait
	explicit, since the old-style implicit wait can now be defeated
	by RCU_FAST_NO_HZ and by rcutorture.)

This approach avoids the false positives encountered when attempting to
use more exact classification of CPU online/offline state.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:06:07 -08:00
Paul E. McKenney
24cd7fd0ea rcu: Update stall-warning documentation
Add documentation of CONFIG_RCU_CPU_STALL_VERBOSE, CONFIG_RCU_CPU_STALL_INFO,
and RCU_STALL_DELAY_DELTA.  Describe multiple stall-warning messages from
a single stall, and the timing of the subsequent messages.  Add headings.
Remove RCU_SECONDS_TILL_STALL_RECHECK because this value is now computed
at runtime from RCU_CPU_STALL_TIMEOUT, so that sysfs changes to the timeout
value now directly affect the RCU_SECONDS_TILL_STALL_RECHECK value.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:03:52 -08:00
Paul E. McKenney
c13f3757d0 rcu: Add CPU-stall capability to rcutorture
Add module parameters to rcutorture that induce a CPU stall.
The stall_cpu parameter specifies how long to stall in seconds,
defaulting to zero, which indicates no stalling is to be undertaken.
The stall_cpu_holdoff parameter specifies how many seconds after
insmod (or boot, if rcutorture is built into the kernel) that this
stall is to start.  The default value for stall_cpu_holdoff is ten
seconds.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:03:52 -08:00
Paul E. McKenney
105617da8d rcu: Make documentation give more realistic rcutorture duration
The torture.txt documentation gives an example rcutorture run with a
100-second duration.  This is ridiculously short, unless maybe testing
a fix for a egregious bug.  Use a more-realistic one-hour duration for
the example.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:03:51 -08:00
Paul E. McKenney
9b9ec9b90e rcutorture: Permit holding off CPU-hotplug operations during boot
When rcutorture is started automatically at boot time, it might well
also start CPU-hotplug operations at that time, which might not be
desirable.  This commit therefore adds an rcutorture parameter that
allows CPU-hotplug operations to be held off for the specified number
of seconds after the start of boot.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:03:50 -08:00
Paul E. McKenney
4c62abc90b rcu: Bring RTFP.txt up to date.
Add publications from 2010 and 2011 to RTFP.txt.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2012-02-21 09:03:21 -08:00
Kees Cook
d493011a37 docs: Additional LWN links to RCU API
Tyler Hicks pointed me at an additional article on RCU and I figured
it should probably be mentioned with the others.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-12-11 10:32:23 -08:00
Paul E. McKenney
b58bdccaa8 rcu: Add rcutorture CPU-hotplug capability
Running CPU-hotplug operations concurrently with rcutorture has
historically been a good way to find bugs in both RCU and CPU hotplug.
This commit therefore adds an rcutorture module parameter called
"onoff_interval" that causes a randomly selected CPU-hotplug operation to
be executed at the specified interval, in seconds.  The default value of
"onoff_interval" is zero, which disables rcutorture-instigated CPU-hotplug
operations.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-12-11 10:31:56 -08:00
Paul E. McKenney
d5f546d834 rcu: Add rcutorture system-shutdown capability
Although it is easy to run rcutorture tests under KVM, there is currently
no nice way to run such a test for a fixed time period, collect all of
the rcutorture data, and then shut the system down cleanly.  This commit
therefore adds an rcutorture module parameter named "shutdown_secs" that
specified the run duration in seconds, after which rcutorture terminates
the test and powers the system down.  The default value for "shutdown_secs"
is zero, which disables shutdown.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-12-11 10:31:46 -08:00
Paul E. McKenney
9ceae0e248 rcu: Add documentation for raw SRCU read-side primitives
Update various files in Documentation/RCU to reflect srcu_read_lock_raw()
and srcu_read_unlock_raw().  Credit to Peter Zijlstra for suggesting
use of the existing _raw suffix instead of the earlier bulkref names.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-12-11 10:31:41 -08:00
Paul E. McKenney
2c01531f08 rcu: Document failing tick as cause of RCU CPU stall warning
One of lclaudio's systems was seeing RCU CPU stall warnings from idle.
These turned out to be caused by a bug that stopped scheduling-clock
tick interrupts from being sent to a given CPU for several hundred seconds.
This commit therefore updates the documentation to call this out as a
possible cause for RCU CPU stall warnings.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-12-11 10:31:26 -08:00
Paul E. McKenney
9b2e4f1880 rcu: Track idleness independent of idle tasks
Earlier versions of RCU used the scheduling-clock tick to detect idleness
by checking for the idle task, but handled idleness differently for
CONFIG_NO_HZ=y.  But there are now a number of uses of RCU read-side
critical sections in the idle task, for example, for tracing.  A more
fine-grained detection of idleness is therefore required.

This commit presses the old dyntick-idle code into full-time service,
so that rcu_idle_enter(), previously known as rcu_enter_nohz(), is
always invoked at the beginning of an idle loop iteration.  Similarly,
rcu_idle_exit(), previously known as rcu_exit_nohz(), is always invoked
at the end of an idle-loop iteration.  This allows the idle task to
use RCU everywhere except between consecutive rcu_idle_enter() and
rcu_idle_exit() calls, in turn allowing architecture maintainers to
specify exactly where in the idle loop that RCU may be used.

Because some of the userspace upcall uses can result in what looks
to RCU like half of an interrupt, it is not possible to expect that
the irq_enter() and irq_exit() hooks will give exact counts.  This
patch therefore expands the ->dynticks_nesting counter to 64 bits
and uses two separate bitfields to count process/idle transitions
and interrupt entry/exit transitions.  It is presumed that userspace
upcalls do not happen in the idle loop or from usermode execution
(though usermode might do a system call that results in an upcall).
The counter is hard-reset on each process/idle transition, which
avoids the interrupt entry/exit error from accumulating.  Overflow
is avoided by the 64-bitness of the ->dyntick_nesting counter.

This commit also adds warnings if a non-idle task asks RCU to enter
idle state (and these checks will need some adjustment before applying
Frederic's OS-jitter patches (http://lkml.org/lkml/2011/10/7/246).
In addition, validation of ->dynticks and ->dynticks_nesting is added.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-12-11 10:31:24 -08:00
Paul E. McKenney
d7bd2d68aa rcu: Document interpretation of RCU-lockdep splats
There has been quite a bit of confusion about what RCU-lockdep splats
mean, so this commit adds some documentation describing how to
interpret them.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:38:28 -07:00
Paul E. McKenney
8cd889cbb6 rcu: Update documentation for additional RCU lockdep functions
Add documentation for rcu_dereference_bh_check(),
rcu_dereference_sched_check(), srcu_dereference_check(), and
rcu_dereference_index_check().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:38:25 -07:00
Michal Hocko
e5177ec77d rcu: Not necessary to pass rcu_read_lock_held() to rcu_dereference_protected()
Since ca5ecddf (rcu: define __rcu address space modifier for sparse)
rcu_dereference_check() use rcu_read_lock_held() as a part of condition
automatically.  Therefore, callers of rcu_dereference_check() no longer
need to pass rcu_read_lock_held() to rcu_dereference_check().

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:38:23 -07:00
Paul E. McKenney
e4cc1f22b2 rcu: Simplify quiescent-state accounting
There is often a delay between the time that a CPU passes through a
quiescent state and the time that this quiescent state is reported to the
RCU core.  It is quite possible that the grace period ended before the
quiescent state could be reported, for example, some other CPU might have
deduced that this CPU passed through dyntick-idle mode.  It is critically
important that quiescent state be counted only against the grace period
that was in effect at the time that the quiescent state was detected.

Previously, this was handled by recording the number of the last grace
period to complete when passing through a quiescent state.  The RCU
core then checks this number against the current value, and rejects
the quiescent state if there is a mismatch.  However, one additional
possibility must be accounted for, namely that the quiescent state was
recorded after the prior grace period completed but before the current
grace period started.  In this case, the RCU core must reject the
quiescent state, but the recorded number will match.  This is handled
when the CPU becomes aware of a new grace period -- at that point,
it invalidates any prior quiescent state.

This works, but is a bit indirect.  The new approach records the current
grace period, and the RCU core checks to see (1) that this is still the
current grace period and (2) that this grace period has not yet ended.
This approach simplifies reasoning about correctness, and this commit
changes over to this new approach.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:38:22 -07:00
Paul E. McKenney
b15a2e7d16 rcu: Fix RCU's NMI documentation
It has long been the case that the architecture must call nmi_enter()
and nmi_exit() rather than irq_enter() and irq_exit() in order to
permit RCU read-side critical sections in NMIs.  Catch the documentation
up with reality.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2011-09-28 21:36:44 -07:00
Paul E. McKenney
bdf2a43649 rcu: Catch rcutorture up to new RCU API additions
Now that the RCU API contains synchronize_rcu_bh(), synchronize_sched(),
call_rcu_sched(), and rcu_bh_expedited()...

Make rcutorture test synchronize_rcu_bh(), getting rid of the old
rcu_bh_torture_synchronize() workaround.  Similarly, make rcutorture test
synchronize_sched(), getting rid of the old sched_torture_synchronize()
workaround.  Make rcutorture test call_rcu_sched() instead of wrappering
synchronize_sched().  Also add testing of rcu_bh_expedited().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:36:43 -07:00
Paul E. McKenney
63cd758e07 rcu: Update rcutorture documentation
Update rcutorture documentation to account for boosting, new types of
RCU torture testing that have been added over the past few years, and
the memory-barrier testing that was added an embarrassingly long time
ago.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:36:39 -07:00
Paul E. McKenney
d5988af531 rcu: Update documentation to flag RCU_BOOST trace information
Call out the RCU_TRACE information that is provided only in kernels
built with RCU_BOOST.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-09-28 21:36:35 -07:00
Wanlong Gao
25eb650a69 doc: fix wrong arch/i386 references
Change all "arch/i386" to "arch/x86" in Documentaion/,
since the directory has changed.

Also update the files which have changed their filename
in the meantime accordingly.

Signed-off-by: Wanlong Gao <wanlong.gao@gmail.com>
[jkosina@suse.cz: reword changelog]
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-06-13 13:43:05 +02:00
Paul E. McKenney
23b5c8fa01 rcu: Decrease memory-barrier usage based on semi-formal proof
(Note: this was reverted, and is now being re-applied in pieces, with
this being the fifth and final piece.  See below for the reason that
it is now felt to be safe to re-apply this.)

Commit d09b62d fixed grace-period synchronization, but left some smp_mb()
invocations in rcu_process_callbacks() that are no longer needed, but
sheer paranoia prevented them from being removed.  This commit removes
them and provides a proof of correctness in their absence.  It also adds
a memory barrier to rcu_report_qs_rsp() immediately before the update to
rsp->completed in order to handle the theoretical possibility that the
compiler or CPU might move massive quantities of code into a lock-based
critical section.  This also proves that the sheer paranoia was not
entirely unjustified, at least from a theoretical point of view.

In addition, the old dyntick-idle synchronization depended on the fact
that grace periods were many milliseconds in duration, so that it could
be assumed that no dyntick-idle CPU could reorder a memory reference
across an entire grace period.  Unfortunately for this design, the
addition of expedited grace periods breaks this assumption, which has
the unfortunate side-effect of requiring atomic operations in the
functions that track dyntick-idle state for RCU.  (There is some hope
that the algorithms used in user-level RCU might be applied here, but
some work is required to handle the NMIs that user-space applications
can happily ignore.  For the short term, better safe than sorry.)

This proof assumes that neither compiler nor CPU will allow a lock
acquisition and release to be reordered, as doing so can result in
deadlock.  The proof is as follows:

1.	A given CPU declares a quiescent state under the protection of
	its leaf rcu_node's lock.

2.	If there is more than one level of rcu_node hierarchy, the
	last CPU to declare a quiescent state will also acquire the
	->lock of the next rcu_node up in the hierarchy,  but only
	after releasing the lower level's lock.  The acquisition of this
	lock clearly cannot occur prior to the acquisition of the leaf
	node's lock.

3.	Step 2 repeats until we reach the root rcu_node structure.
	Please note again that only one lock is held at a time through
	this process.  The acquisition of the root rcu_node's ->lock
	must occur after the release of that of the leaf rcu_node.

4.	At this point, we set the ->completed field in the rcu_state
	structure in rcu_report_qs_rsp().  However, if the rcu_node
	hierarchy contains only one rcu_node, then in theory the code
	preceding the quiescent state could leak into the critical
	section.  We therefore precede the update of ->completed with a
	memory barrier.  All CPUs will therefore agree that any updates
	preceding any report of a quiescent state will have happened
	before the update of ->completed.

5.	Regardless of whether a new grace period is needed, rcu_start_gp()
	will propagate the new value of ->completed to all of the leaf
	rcu_node structures, under the protection of each rcu_node's ->lock.
	If a new grace period is needed immediately, this propagation
	will occur in the same critical section that ->completed was
	set in, but courtesy of the memory barrier in #4 above, is still
	seen to follow any pre-quiescent-state activity.

6.	When a given CPU invokes __rcu_process_gp_end(), it becomes
	aware of the end of the old grace period and therefore makes
	any RCU callbacks that were waiting on that grace period eligible
	for invocation.

	If this CPU is the same one that detected the end of the grace
	period, and if there is but a single rcu_node in the hierarchy,
	we will still be in the single critical section.  In this case,
	the memory barrier in step #4 guarantees that all callbacks will
	be seen to execute after each CPU's quiescent state.

	On the other hand, if this is a different CPU, it will acquire
	the leaf rcu_node's ->lock, and will again be serialized after
	each CPU's quiescent state for the old grace period.

On the strength of this proof, this commit therefore removes the memory
barriers from rcu_process_callbacks() and adds one to rcu_report_qs_rsp().
The effect is to reduce the number of memory barriers by one and to
reduce the frequency of execution from about once per scheduling tick
per CPU to once per grace period.

This was reverted do to hangs found during testing by Yinghai Lu and
Ingo Molnar.  Frederic Weisbecker supplied Yinghai with tracing that
located the underlying problem, and Frederic also provided the fix.

The underlying problem was that the HARDIRQ_ENTER() macro from
lib/locking-selftest.c invoked irq_enter(), which in turn invokes
rcu_irq_enter(), but HARDIRQ_EXIT() invoked __irq_exit(), which
does not invoke rcu_irq_exit().  This situation resulted in calls
to rcu_irq_enter() that were not balanced by the required calls to
rcu_irq_exit().  Therefore, after these locking selftests completed,
RCU's dyntick-idle nesting count was a large number (for example,
72), which caused RCU to to conclude that the affected CPU was not in
dyntick-idle mode when in fact it was.

RCU would therefore incorrectly wait for this dyntick-idle CPU, resulting
in hangs.

In contrast, with Frederic's patch, which replaces the irq_enter()
in HARDIRQ_ENTER() with an __irq_enter(), these tests don't ever call
either rcu_irq_enter() or rcu_irq_exit(), which works because the CPU
running the test is already marked as not being in dyntick-idle mode.
This means that the rcu_irq_enter() and rcu_irq_exit() calls and RCU
then has no problem working out which CPUs are in dyntick-idle mode and
which are not.

The reason that the imbalance was not noticed before the barrier patch
was applied is that the old implementation of rcu_enter_nohz() ignored
the nesting depth.  This could still result in delays, but much shorter
ones.  Whenever there was a delay, RCU would IPI the CPU with the
unbalanced nesting level, which would eventually result in rcu_enter_nohz()
being called, which in turn would force RCU to see that the CPU was in
dyntick-idle mode.

The reason that very few people noticed the problem is that the mismatched
irq_enter() vs. __irq_exit() occured only when the kernel was built with
CONFIG_DEBUG_LOCKING_API_SELFTESTS.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-26 09:42:23 -07:00
Paul E. McKenney
80d02085d9 Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
This reverts commit e59fb3120b.

This reversion was due to (extreme) boot-time slowdowns on SPARC seen by
Yinghai Lu and on x86 by Ingo
.
This is a non-trivial reversion due to intervening commits.

Conflicts:

	Documentation/RCU/trace.txt
	kernel/rcutree.c

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-05-19 23:25:29 +02:00
Paul E. McKenney
5ece5bab3e rcu: Add forward-progress diagnostic for per-CPU kthreads
Increment a per-CPU counter on each pass through rcu_cpu_kthread()'s
service loop, and add it to the rcudata trace output.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:57 -07:00
Paul E. McKenney
15ba0ba860 rcu: add grace-period age and more kthread state to tracing
This commit adds the age in jiffies of the current grace period along
with the duration in jiffies of the longest grace period since boot
to the rcu/rcugp debugfs file.  It also adds an additional "O" state
to kthread tracing to differentiate between the kthread waiting due to
having nothing to do on the one hand and waiting due to being on the
wrong CPU on the other hand.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-05-05 23:16:56 -07:00
Paul E. McKenney
90e6ac3657 rcu: update tracing documentation for new rcutorture and rcuboost
This commit documents the new debugfs rcu/rcutorture and rcu/rcuboost
trace files.  The description has been updated as suggested by Josh
Triplett.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-05-05 23:16:56 -07:00
Paul E. McKenney
0ac3d136b2 rcu: add callback-queue information to rcudata output
This commit adds an indication of the state of the callback queue using
a string of four characters following the "ql=" integer queue length.
The first character is "N" if there are callbacks that have been
queued that are not yet ready to be handled by the next grace period, or
"." otherwise.  The second character is "R" if there are callbacks queued
that are ready to be handled by the next grace period, or "." otherwise.
The third character is "W" if there are callbacks waiting for the current
grace period, or "." otherwise.  Finally, the fourth character is "D"
if there are callbacks that have been handled by a prior grace period
and are waiting to be invoked, or ".".

Note that callbacks that are in the process of being invoked are
not shown.  These callbacks would have been removed from the rcu_data
structure's list by rcu_do_batch() prior to being executed.  (These
callbacks are also not reflected in the "ql=" total, FWIW.)

Also, document the new callback-queue trace information.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:56 -07:00
Paul E. McKenney
2fa218d8bb rcu: Update RCU's trace.txt documentation for new format
The trace.txt file had obsolete output for the debugfs rcu/rcudata
file, so update it.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:56 -07:00
Paul E. McKenney
12f5f524ca rcu: merge TREE_PREEPT_RCU blocked_tasks[] lists
Combine the current TREE_PREEMPT_RCU ->blocked_tasks[] lists in the
rcu_node structure into a single ->blkd_tasks list with ->gp_tasks
and ->exp_tasks tail pointers.  This is in preparation for RCU priority
boosting, which will add a third dimension to the combinatorial explosion
in the ->blocked_tasks[] case, but simply a third pointer in the new
->blkd_tasks case.

Also update documentation to reflect blocked_tasks[] merge

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:54 -07:00
Paul E. McKenney
e59fb3120b rcu: Decrease memory-barrier usage based on semi-formal proof
Commit d09b62d fixed grace-period synchronization, but left some smp_mb()
invocations in rcu_process_callbacks() that are no longer needed, but
sheer paranoia prevented them from being removed.  This commit removes
them and provides a proof of correctness in their absence.  It also adds
a memory barrier to rcu_report_qs_rsp() immediately before the update to
rsp->completed in order to handle the theoretical possibility that the
compiler or CPU might move massive quantities of code into a lock-based
critical section.  This also proves that the sheer paranoia was not
entirely unjustified, at least from a theoretical point of view.

In addition, the old dyntick-idle synchronization depended on the fact
that grace periods were many milliseconds in duration, so that it could
be assumed that no dyntick-idle CPU could reorder a memory reference
across an entire grace period.  Unfortunately for this design, the
addition of expedited grace periods breaks this assumption, which has
the unfortunate side-effect of requiring atomic operations in the
functions that track dyntick-idle state for RCU.  (There is some hope
that the algorithms used in user-level RCU might be applied here, but
some work is required to handle the NMIs that user-space applications
can happily ignore.  For the short term, better safe than sorry.)

This proof assumes that neither compiler nor CPU will allow a lock
acquisition and release to be reordered, as doing so can result in
deadlock.  The proof is as follows:

1.	A given CPU declares a quiescent state under the protection of
	its leaf rcu_node's lock.

2.	If there is more than one level of rcu_node hierarchy, the
	last CPU to declare a quiescent state will also acquire the
	->lock of the next rcu_node up in the hierarchy,  but only
	after releasing the lower level's lock.  The acquisition of this
	lock clearly cannot occur prior to the acquisition of the leaf
	node's lock.

3.	Step 2 repeats until we reach the root rcu_node structure.
	Please note again that only one lock is held at a time through
	this process.  The acquisition of the root rcu_node's ->lock
	must occur after the release of that of the leaf rcu_node.

4.	At this point, we set the ->completed field in the rcu_state
	structure in rcu_report_qs_rsp().  However, if the rcu_node
	hierarchy contains only one rcu_node, then in theory the code
	preceding the quiescent state could leak into the critical
	section.  We therefore precede the update of ->completed with a
	memory barrier.  All CPUs will therefore agree that any updates
	preceding any report of a quiescent state will have happened
	before the update of ->completed.

5.	Regardless of whether a new grace period is needed, rcu_start_gp()
	will propagate the new value of ->completed to all of the leaf
	rcu_node structures, under the protection of each rcu_node's ->lock.
	If a new grace period is needed immediately, this propagation
	will occur in the same critical section that ->completed was
	set in, but courtesy of the memory barrier in #4 above, is still
	seen to follow any pre-quiescent-state activity.

6.	When a given CPU invokes __rcu_process_gp_end(), it becomes
	aware of the end of the old grace period and therefore makes
	any RCU callbacks that were waiting on that grace period eligible
	for invocation.

	If this CPU is the same one that detected the end of the grace
	period, and if there is but a single rcu_node in the hierarchy,
	we will still be in the single critical section.  In this case,
	the memory barrier in step #4 guarantees that all callbacks will
	be seen to execute after each CPU's quiescent state.

	On the other hand, if this is a different CPU, it will acquire
	the leaf rcu_node's ->lock, and will again be serialized after
	each CPU's quiescent state for the old grace period.

On the strength of this proof, this commit therefore removes the memory
barriers from rcu_process_callbacks() and adds one to rcu_report_qs_rsp().
The effect is to reduce the number of memory barriers by one and to
reduce the frequency of execution from about once per scheduling tick
per CPU to once per grace period.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:54 -07:00
Paul E. McKenney
a00e0d714f rcu: Remove conditional compilation for RCU CPU stall warnings
The RCU CPU stall warnings can now be controlled using the
rcu_cpu_stall_suppress boot-time parameter or via the same parameter
from sysfs.  There is therefore no longer any reason to have
kernel config parameters for this feature.  This commit therefore
removes the RCU_CPU_STALL_DETECTOR and RCU_CPU_STALL_DETECTOR_RUNNABLE
kernel config parameters.  The RCU_CPU_STALL_TIMEOUT parameter remains
to allow the timeout to be tuned and the RCU_CPU_STALL_VERBOSE parameter
remains to allow task-stall information to be suppressed if desired.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2011-05-05 23:16:54 -07:00
Paul E. McKenney
fea651267e rcu: add documentation saying which RCU flavor to choose
Reported-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2011-03-04 08:05:25 -08:00
Paul E. McKenney
2d999e03b7 rcu: update documentation/comments for Lai's adoption patch
Lai's RCU-callback immediate-adoption patch changes the RCU tracing
output, so update tracing.txt.  Also update a few comments to clarify
the synchronization design.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-11-29 22:01:59 -08:00
Paul E. McKenney
8e79e1f961 rcu: document TINY_RCU and TINY_PREEMPT_RCU tracing.
Add the required verbiage to Documentation/RCU/trace.txt.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-11-29 22:01:56 -08:00
Paul E. McKenney
269dcc1c2e rcu: Add tracing data to support queueing models
The current tracing data is not sufficient to deduce the average time
that a callback spends waiting for a grace period to end.  Add three
per-CPU counters recording the number of callbacks invoked (ci), the
number of callbacks orphaned (co), and the number of callbacks adopted
(ca).  Given the existing callback queue length (ql), the average wait
time in absence of CPU hotplug operations is ql/ci.  The units of wait
time will be in terms of the duration over which ci was measured.

In the presence of CPU hotplug operations, there is room for argument,
but ql/(ci-co+ca) won't steer you too far wrong.

Also fixes a typo called out by Lucas De Marchi <lucas.de.marchi@gmail.com>.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-09-23 09:16:53 -07:00
Paul E. McKenney
2c96c7751d rcu: upgrade stallwarn.txt documentation for CPU-bound RT processes
CPU-bound real-time processes can cause RCU CPU stall warnings, and
much other trouble as well.  Document the fact that they can cause
RCU CPU stall warnings.

Suggested-by: Darren Hart <dvhltc@us.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-08-23 16:34:02 -07:00
Paul E. McKenney
5cc6517abd rcu: document ways of stalling updates in low-memory situations
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-08-20 09:00:14 -07:00
Paul E. McKenney
84483ea42c rcu: add shiny new debug assists to Documentation/RCU/checklist.txt
Add a section describing PROVE_RCU, DEBUG_OBJECTS_RCU_HEAD, and
the __rcu sparse checking to the RCU checklist.

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2010-08-19 17:18:01 -07:00
Justin P. Mattock
0ea6e61122 Documentation: update broken web addresses.
Below you will find an updated version from the original series bunching all patches into one big patch
updating broken web addresses that are located in Documentation/*
Some of the addresses date as far far back as 1995 etc... so searching became a bit difficult,
the best way to deal with these is to use web.archive.org to locate these addresses that are outdated.
Now there are also some addresses pointing to .spec files some are located, but some(after searching
on the companies site)where still no where to be found. In this case I just changed the address
to the company site this way the users can contact the company and they can locate them for the users.

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Thomas Weber <weber@corscience.de>
Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Cc: Paulo Marques <pmarques@grupopie.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Michael Neuling <mikey@neuling.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2010-08-04 15:21:40 +02:00
Linus Torvalds
b8ae30ee26 Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (49 commits)
  stop_machine: Move local variable closer to the usage site in cpu_stop_cpu_callback()
  sched, wait: Use wrapper functions
  sched: Remove a stale comment
  ondemand: Make the iowait-is-busy time a sysfs tunable
  ondemand: Solve a big performance issue by counting IOWAIT time as busy
  sched: Intoduce get_cpu_iowait_time_us()
  sched: Eliminate the ts->idle_lastupdate field
  sched: Fold updating of the last_update_time_info into update_ts_time_stats()
  sched: Update the idle statistics in get_cpu_idle_time_us()
  sched: Introduce a function to update the idle statistics
  sched: Add a comment to get_cpu_idle_time_us()
  cpu_stop: add dummy implementation for UP
  sched: Remove rq argument to the tracepoints
  rcu: need barrier() in UP synchronize_sched_expedited()
  sched: correctly place paranioa memory barriers in synchronize_sched_expedited()
  sched: kill paranoia check in synchronize_sched_expedited()
  sched: replace migration_thread with cpu_stop
  stop_machine: reimplement using cpu_stop
  cpu_stop: implement stop_cpu[s]()
  sched: Fix select_idle_sibling() logic in select_task_rq_fair()
  ...
2010-05-18 08:27:54 -07:00
Paul E. McKenney
f1d507beea rcu: improve the RCU CPU-stall warning documentation
The existing Documentation/RCU/stallwarn.txt has proven unhelpful, so
rework it a bit.  In particular, show how to interpret the stall-warning
messages.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-05-10 11:08:35 -07:00
Paul E. McKenney
d21670acab rcu: reduce the number of spurious RCU_SOFTIRQ invocations
Lai Jiangshan noted that up to 10% of the RCU_SOFTIRQ are spurious, and
traced this down to the fact that the current grace-period machinery
will uselessly raise RCU_SOFTIRQ when a given CPU needs to go through
a quiescent state, but has not yet done so.  In this situation, there
might well be nothing that RCU_SOFTIRQ can do, and the overhead can be
worth worrying about in the ksoftirqd case.  This patch therefore avoids
raising RCU_SOFTIRQ in this situation.

Changes since v1 (http://lkml.org/lkml/2010/3/30/122 from Lai Jiangshan):

o	Omit the rcu_qs_pending() prechecks, as they aren't that
	much less expensive than the quiescent-state checks.

o	Merge with the set_need_resched() patch that reduces IPIs.

o	Add the new n_rp_report_qs field to the rcu_pending tracing output.

o	Update the tracing documentation accordingly.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2010-05-10 11:08:35 -07:00
Ingo Molnar
e7858f52a5 Merge branch 'cpu_stop' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc into sched/core 2010-05-08 18:11:19 +02:00
Tejun Heo
969c79215a sched: replace migration_thread with cpu_stop
Currently migration_thread is serving three purposes - migration
pusher, context to execute active_load_balance() and forced context
switcher for expedited RCU synchronize_sched.  All three roles are
hardcoded into migration_thread() and determining which job is
scheduled is slightly messy.

This patch kills migration_thread and replaces all three uses with
cpu_stop.  The three different roles of migration_thread() are
splitted into three separate cpu_stop callbacks -
migration_cpu_stop(), active_load_balance_cpu_stop() and
synchronize_sched_expedited_cpu_stop() - and each use case now simply
asks cpu_stop to execute the callback as necessary.

synchronize_sched_expedited() was implemented with private
preallocated resources and custom multi-cpu queueing and waiting
logic, both of which are provided by cpu_stop.
synchronize_sched_expedited_count is made atomic and all other shared
resources along with the mutex are dropped.

synchronize_sched_expedited() also implemented a check to detect cases
where not all the callback got executed on their assigned cpus and
fall back to synchronize_sched().  If called with cpu hotplug blocked,
cpu_stop already guarantees that and the condition cannot happen;
otherwise, stop_machine() would break.  However, this patch preserves
the paranoid check using a cpumask to record on which cpus the stopper
ran so that it can serve as a bisection point if something actually
goes wrong theree.

Because the internal execution state is no longer visible,
rcu_expedited_torture_stats() is removed.

This patch also renames cpu_stop threads to from "stopper/%d" to
"migration/%d".  The names of these threads ultimately don't matter
and there's no reason to make unnecessary userland visible changes.

With this patch applied, stop_machine() and sched now share the same
resources.  stop_machine() is faster without wasting any resources and
sched migration users are much cleaner.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Josh Triplett <josh@freedesktop.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
2010-05-06 18:49:21 +02:00
Paul E. McKenney
50aec0024e rcu: Update docs for rcu_access_pointer and rcu_dereference_protected
Update examples and lists of APIs to include these new
primitives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: eric.dumazet@gmail.com
LKML-Reference: <1270852752-25278-3-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-04-14 12:20:12 +02:00
Paul E. McKenney
1bd22e374b rcu: Use canonical URL for Mathieu's dissertation
The version numbers change too quickly, so use a canonical URL
that represents the most recent version.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-16-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-02-25 10:34:56 +01:00
Paul E. McKenney
998f2ac3fe rcu: Fix citation of Mathieu's dissertation
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-14-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-02-25 10:34:54 +01:00