Commit Graph

192 Commits

Author SHA1 Message Date
Wang Qing
b124ac45bd kernel: watchdog: modify the explanation related to watchdog thread
The watchdog thread has been replaced by cpu_stop_work, modify the
explanation related.

Link: https://lkml.kernel.org/r/1619687073-24686-2-git-send-email-wangqing@vivo.com
Signed-off-by: Wang Qing <wangqing@vivo.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: "Guilherme G. Piccoli" <gpiccoli@canonical.com>
Cc: Qais Yousef <qais.yousef@arm.com>
Cc: Santosh Sivaraj <santosh@fossix.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-29 10:53:46 -07:00
Petr Mladek
0f90b88dbc watchdog: reliable handling of timestamps
Commit 9bf3bc949f ("watchdog: cleanup handling of false positives")
tried to handle a virtual host stopped by the host a more
straightforward and cleaner way.

But it introduced a risk of false softlockup reports.  The virtual host
might be stopped at any time, for example between
kvm_check_and_clear_guest_paused() and is_softlockup().  As a result,
is_softlockup() might read the updated jiffies and detects a softlockup.

A solution might be to put back kvm_check_and_clear_guest_paused() after
is_softlockup() and detect it.  But it would put back the cycle that
complicates the logic.

In fact, the handling of all the timestamps is not reliable.  The code
does not guarantee when and how many times the timestamps are read.  For
example, "period_ts" might be touched anytime also from NMI and re-read in
is_softlockup().  It works just by chance.

Fix all the problems by making the code even more explicit.

1. Make sure that "now" and "period_ts" timestamps are read only once.
   They might be changed at anytime by NMI or when the virtual guest is
   stopped by the host.  Note that "now" timestamp does this implicitly
   because "jiffies" is marked volatile.

2. "now" time must be read first.  The state of "period_ts" will
   decide whether it will be used or the period will get restarted.

3. kvm_check_and_clear_guest_paused() must be called before reading
   "period_ts".  It touches the variable when the guest was stopped.

As a result, "now" timestamp is used only when the watchdog was not
touched and the guest not stopped in the meantime.  "period_ts" is
restarted in all other situations.

Link: https://lkml.kernel.org/r/YKT55gw+RZfyoFf7@alley
Fixes: 9bf3bc949f ("watchdog: cleanup handling of false positives")
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reported-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-22 15:09:07 -10:00
Petr Mladek
9bf3bc949f watchdog: cleanup handling of false positives
Commit d6ad3e286d ("softlockup: Add sched_clock_tick() to avoid kernel
warning on kgdb resume") introduced touch_softlockup_watchdog_sync().

It solved a problem when the watchdog was touched in an atomic context,
the timer callback was proceed right after releasing interrupts, and the
local clock has not been updated yet.  In this case, sched_clock_tick()
was called in watchdog_timer_fn() before updating the timer.

So far so good.

Later commit 5d1c0f4a80 ("watchdog: add check for suspended vm in
softlockup detector") added two kvm_check_and_clear_guest_paused()
calls.  They touch the watchdog when the guest has been sleeping.

The code makes my head spin around.

Scenario 1:

    + guest did sleep:
	+ PVCLOCK_GUEST_STOPPED is set

    + 1st watchdog_timer_fn() invocation:
	+ the watchdog is not touched yet
	+ is_softlockup() returns too big delay
	+ kvm_check_and_clear_guest_paused():
	   + clear PVCLOCK_GUEST_STOPPED
	   + call touch_softlockup_watchdog_sync()
		+ set SOFTLOCKUP_DELAY_REPORT
		+ set softlockup_touch_sync
	+ return from the timer callback

      + 2nd watchdog_timer_fn() invocation:

	+ call sched_clock_tick() even though it is not needed.
	  The timer callback was invoked again only because the clock
	  has already been updated in the meantime.

	+ call kvm_check_and_clear_guest_paused() that does nothing
	  because PVCLOCK_GUEST_STOPPED has been cleared already.

	+ call update_report_ts() and return. This is fine. Except
	  that sched_clock_tick() might allow to set it already
	  during the 1st invocation.

Scenario 2:

	+ guest did sleep

	+ 1st watchdog_timer_fn() invocation
	    + same as in 1st scenario

	+ guest did sleep again:
	    + set PVCLOCK_GUEST_STOPPED again

	+ 2nd watchdog_timer_fn() invocation
	    + SOFTLOCKUP_DELAY_REPORT is set from 1st invocation
	    + call sched_clock_tick()
	    + call kvm_check_and_clear_guest_paused()
		+ clear PVCLOCK_GUEST_STOPPED
		+ call touch_softlockup_watchdog_sync()
		    + set SOFTLOCKUP_DELAY_REPORT
		    + set softlockup_touch_sync
	    + call update_report_ts() (set real timestamp immediately)
	    + return from the timer callback

	+ 3rd watchdog_timer_fn() invocation
	    + timestamp is set from 2nd invocation
	    + softlockup_touch_sync is set but not checked because
	      the real timestamp is already set

Make the code more straightforward:

1. Always call kvm_check_and_clear_guest_paused() at the very
   beginning to handle PVCLOCK_GUEST_STOPPED. It touches the watchdog
   when the quest did sleep.

2. Handle the situation when the watchdog has been touched
   (SOFTLOCKUP_DELAY_REPORT is set).

   Call sched_clock_tick() when touch_*sync() variant was used. It makes
   sure that the timestamp will be up to date even when it has been
   touched in atomic context or quest did sleep.

As a result, kvm_check_and_clear_guest_paused() is called on a single
location.  And the right timestamp is always set when returning from the
timer callback.

Link: https://lkml.kernel.org/r/20210311122130.6788-7-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:36 -07:00
Petr Mladek
9f113bf760 watchdog: fix barriers when printing backtraces from all CPUs
Any parallel softlockup reports are skipped when one CPU is already
printing backtraces from all CPUs.

The exclusive rights are synchronized using one bit in
soft_lockup_nmi_warn.  There is also one memory barrier that does not make
much sense.

Use two barriers on the right location to prevent mixing two reports.

[pmladek@suse.com: use bit lock operations to prevent multiple soft-lockup reports]
  Link: https://lkml.kernel.org/r/YFSVsLGVWMXTvlbk@alley

Link: https://lkml.kernel.org/r/20210311122130.6788-6-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:36 -07:00
Petr Mladek
1bc503cb4a watchdog/softlockup: remove logic that tried to prevent repeated reports
The softlockup detector does some gymnastic with the variable
soft_watchdog_warn.  It was added by the commit 58687acba5
("lockup_detector: Combine nmi_watchdog and softlockup detector").

The purpose is not completely clear.  There are the following clues.  They
describe the situation how it looked after the above mentioned commit:

  1. The variable was checked with a comment "only warn once".

  2. The variable was set when softlockup was reported. It was cleared
     only when the CPU was not longer in the softlockup state.

  3. watchdog_touch_ts was not explicitly updated when the softlockup
     was reported. Without this variable, the report would normally
     be printed again during every following watchdog_timer_fn()
     invocation.

The logic has got even more tangled up by the commit ed235875e2
("kernel/watchdog.c: print traces for all cpus on lockup detection").
After this commit, soft_watchdog_warn is set only when
softlockup_all_cpu_backtrace is enabled.  But multiple reports from all
CPUs are prevented by a new variable soft_lockup_nmi_warn.

Conclusion:

The variable probably never worked as intended.  In each case, it has not
worked last many years because the softlockup was reported repeatedly
after the full period defined by watchdog_thresh.

The reason is that watchdog gets touched in many known slow paths, for
example, in printk_stack_address().  This code is called also when
printing the softlockup report.  It means that the watchdog timestamp gets
updated after each report.

Solution:

Simply remove the logic. People want the periodic report anyway.

Link: https://lkml.kernel.org/r/20210311122130.6788-5-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:36 -07:00
Petr Mladek
fef06efc2e watchdog/softlockup: report the overall time of softlockups
The softlockup detector currently shows the time spent since the last
report.  As a result it is not clear whether a CPU is infinitely hogged by
a single task or if it is a repeated event.

The situation can be simulated with a simply busy loop:

	while (true)
	      cpu_relax();

The softlockup detector produces:

[  168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
[  196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
[  236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865]

But it should be, something like:

[  480.372418] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4943]
[  508.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 52s! [cat:4943]
[  548.372359] watchdog: BUG: soft lockup - CPU#2 stuck for 89s! [cat:4943]
[  576.372351] watchdog: BUG: soft lockup - CPU#2 stuck for 115s! [cat:4943]

For the better output, add an additional timestamp of the last report.
Only this timestamp is reset when the watchdog is intentionally touched
from slow code paths or when printing the report.

Link: https://lkml.kernel.org/r/20210311122130.6788-4-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:36 -07:00
Petr Mladek
c9ad17c991 watchdog: explicitly update timestamp when reporting softlockup
The softlockup situation might stay for a long time or even forever.  When
it happens, the softlockup debug messages are printed in regular intervals
defined by get_softlockup_thresh().

There is a mystery.  The repeated message is printed after the full
interval that is defined by get_softlockup_thresh().  But the timer
callback is called more often as defined by sample_period.  The code looks
like the soflockup should get reported in every sample_period when it was
once behind the thresh.

It works only by chance.  The watchdog is touched when printing the stall
report, for example, in printk_stack_address().

Make the behavior clear and predictable by explicitly updating the
timestamp in watchdog_timer_fn() when the report gets printed.

Link: https://lkml.kernel.org/r/20210311122130.6788-3-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:35 -07:00
Petr Mladek
7c0012f522 watchdog: rename __touch_watchdog() to a better descriptive name
Patch series "watchdog/softlockup: Report overall time and some cleanup", v2.

I dug deep into the softlockup watchdog history when time permitted this
year.  And reworked the patchset that fixed timestamps and cleaned up the
code[2].

I split it into very small steps and did even more code clean up.  The
result looks quite strightforward and I am pretty confident with the
changes.

[1] v2: https://lore.kernel.org/r/20201210160038.31441-1-pmladek@suse.com
[2] v1: https://lore.kernel.org/r/20191024114928.15377-1-pmladek@suse.com

This patch (of 6):

There are many touch_*watchdog() functions.  They are called in situations
where the watchdog could report false positives or create unnecessary
noise.  For example, when CPU is entering idle mode, a virtual machine is
stopped, or a lot of messages are printed in the atomic context.

These functions set SOFTLOCKUP_RESET instead of a real timestamp.  It
allows to call them even in a context where jiffies might be outdated.
For example, in an atomic context.

The real timestamp is set by __touch_watchdog() that is called from the
watchdog timer callback.

Rename this callback to update_touch_ts().  It better describes the effect
and clearly distinguish is from the other touch_*watchdog() functions.

Another motivation is that two timestamps are going to be used.  One will
be used for the total softlockup time.  The other will be used to measure
time since the last report.  The new function name will help to
distinguish which timestamp is being updated.

Link: https://lkml.kernel.org/r/20210311122130.6788-1-pmladek@suse.com
Link: https://lkml.kernel.org/r/20210311122130.6788-2-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-04-30 11:20:35 -07:00
Wang Qing
89e28ce60c workqueue/watchdog: Make unbound workqueues aware of touch_softlockup_watchdog()
84;0;0c84;0;0c
There are two workqueue-specific watchdog timestamps:

    + @wq_watchdog_touched_cpu (per-CPU) updated by
      touch_softlockup_watchdog()

    + @wq_watchdog_touched (global) updated by
      touch_all_softlockup_watchdogs()

watchdog_timer_fn() checks only the global @wq_watchdog_touched for
unbound workqueues. As a result, unbound workqueues are not aware
of touch_softlockup_watchdog(). The watchdog might report a stall
even when the unbound workqueues are blocked by a known slow code.

Solution:
touch_softlockup_watchdog() must touch also the global @wq_watchdog_touched
timestamp.

The global timestamp can no longer be used for bound workqueues because
it is now updated from all CPUs. Instead, bound workqueues have to check
only @wq_watchdog_touched_cpu and these timestamps have to be updated for
all CPUs in touch_all_softlockup_watchdogs().

Beware:
The change might cause the opposite problem. An unbound workqueue
might get blocked on CPU A because of a real softlockup. The workqueue
watchdog would miss it when the timestamp got touched on CPU B.

It is acceptable because softlockups are detected by softlockup
watchdog. The workqueue watchdog is there to detect stalls where
a work never finishes, for example, because of dependencies of works
queued into the same workqueue.

V3:
- Modify the commit message clearly according to Petr's suggestion.

Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2021-04-04 13:26:49 -04:00
Santosh Sivaraj
e7e046155a kernel/watchdog: fix watchdog_allowed_mask not used warning
Define watchdog_allowed_mask only when SOFTLOCKUP_DETECTOR is enabled.

Fixes: 7feeb9cd4f ("watchdog/sysctl: Clean up sysctl variable name space")
Signed-off-by: Santosh Sivaraj <santosh@fossix.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20201106015025.1281561-1-santosh@fossix.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-11-14 11:26:03 -08:00
Guilherme G. Piccoli
f117955a22 kernel/watchdog.c: convert {soft/hard}lockup boot parameters to sysctl aliases
After a recent change introduced by Vlastimil's series [0], kernel is
able now to handle sysctl parameters on kernel command line; also, the
series introduced a simple infrastructure to convert legacy boot
parameters (that duplicate sysctls) into sysctl aliases.

This patch converts the watchdog parameters softlockup_panic and
{hard,soft}lockup_all_cpu_backtrace to use the new alias infrastructure.
It fixes the documentation too, since the alias only accepts values 0 or
1, not the full range of integers.

We also took the opportunity here to improve the documentation of the
previously converted hung_task_panic (see the patch series [0]) and put
the alias table in alphabetical order.

[0] http://lkml.kernel.org/r/20200427180433.7029-1-vbabka@suse.cz

Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Link: http://lkml.kernel.org/r/20200507214624.21911-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 11:05:56 -07:00
Christoph Hellwig
32927393dc sysctl: pass kernel pointers to ->proc_handler
Instead of having all the sysctl handlers deal with user pointers, which
is rather hairy in terms of the BPF interaction, copy the input to and
from  userspace in common code.  This also means that the strings are
always NUL-terminated by the common code, making the API a little bit
safer.

As most handler just pass through the data to one of the common handlers
a lot of the changes are mechnical.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-27 02:07:40 -04:00
Thomas Gleixner
11e31f608b watchdog/softlockup: Enforce that timestamp is valid on boot
Robert reported that during boot the watchdog timestamp is set to 0 for one
second which is the indicator for a watchdog reset.

The reason for this is that the timestamp is in seconds and the time is
taken from sched clock and divided by ~1e9. sched clock starts at 0 which
means that for the first second during boot the watchdog timestamp is 0,
i.e. reset.

Use ULONG_MAX as the reset indicator value so the watchdog works correctly
right from the start. ULONG_MAX would only conflict with a real timestamp
if the system reaches an uptime of 136 years on 32bit and almost eternity
on 64bit.

Reported-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/87o8v3uuzl.fsf@nanos.tec.linutronix.de
2020-01-17 11:19:22 +01:00
Petr Mladek
3a51449b79 watchdog/softlockup: Remove obsolete check of last reported task
commit 9cf57731b6 ("watchdog/softlockup: Replace "watchdog/%u" threads
 with cpu_stop_work") ensures that the watchdog is reliably touched during
a task switch.

As a result the check for an unnoticed task switch is not longer needed.

Remove the relevant code, which effectively reverts commit b1a8de1f53
("softlockup: make detector be aware of task switch of processes hogging
cpu")

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Ziljstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20191024114928.15377-2-pmladek@suse.com
2020-01-16 14:52:48 +01:00
Jisheng Zhang
d129479f1f watchdog: Remove soft_lockup_hrtimer_cnt and related code
After commit 9cf57731b6 ("watchdog/softlockup: Replace "watchdog/%u"
threads with cpu_stop_work"), the percpu soft_lockup_hrtimer_cnt is
not used any more, so remove it and related code.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191218131720.4146aea2@xhacker.debian
2020-01-16 12:25:51 +01:00
Sebastian Andrzej Siewior
d2ab4cf494 watchdog: Mark watchdog_hrtimer to expire in hard interrupt context
The watchdog hrtimer must expire in hard interrupt context even on
PREEMPT_RT=y kernels as otherwise the hard/softlockup detection logic would
not work.

No functional change.

[ tglx: Split out from larger combo patch. Added changelog ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190726185753.262895510@linutronix.de
2019-08-01 20:51:20 +02:00
Arash Fotouhi
76e1552466 watchdog: Fix typo in comment
Signed-off-by: Arash Fotouhi <arash@arashfotouhi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: loberman@redhat.com
Cc: vincent.whitchurch@axis.com
Link: http://lkml.kernel.org/r/1553308112-3513-1-git-send-email-arash@arashfotouhi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-18 14:05:51 +02:00
Thomas Gleixner
7dd4761711 watchdog: Respect watchdog cpumask on CPU hotplug
The rework of the watchdog core to use cpu_stop_work broke the watchdog
cpumask on CPU hotplug.

The watchdog_enable/disable() functions are now called unconditionally from
the hotplug callback, i.e. even on CPUs which are not in the watchdog
cpumask. As a consequence the watchdog can become unstoppable.

Only invoke them when the plugged CPU is in the watchdog cpumask.

Fixes: 9cf57731b6 ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Reported-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1903262245490.1789@nanos.tec.linutronix.de
2019-03-28 13:32:01 +01:00
Valdis Kletnieks
48084abf21 watchdog/core: Make variables static
sparse complains:
  CHECK   kernel/watchdog.c
kernel/watchdog.c:45:19: warning: symbol 'nmi_watchdog_available'
			 	  was not declared. Should it be static?
kernel/watchdog.c:47:16: warning: symbol 'watchdog_allowed_mask'
			 	  was not declared. Should it be static?

They're not referenced by name from anyplace else, make them static.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/7855.1552383228@turing-police
2019-03-22 13:40:17 +01:00
Laurence Oberman
1129505552 watchdog/core: Add watchdog_thresh command line parameter
The hard and soft lockup detector threshold has a default value of 10
seconds which can only be changed via sysctl.

During early boot lockup detection can trigger when noisy debugging emits
a large amount of messages to the console, but there is no way to set a
larger threshold on the kernel command line. The detector can only be
completely disabled.

Add a new watchdog_thresh= command line parameter to allow boot time
control over the threshold. It works in the same way as the sysctl and
affects both the soft and the hard lockup detectors.

Signed-off-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: rdunlap@infradead.org
Cc: prarit@redhat.com
Link: https://lkml.kernel.org/r/1541079018-13953-1-git-send-email-loberman@redhat.com
2018-11-01 14:33:35 +01:00
Vincent Whitchurch
cb9d7fd51d watchdog: Mark watchdog touch functions as notrace
Some architectures need to use stop_machine() to patch functions for
ftrace, and the assumption is that the stopped CPUs do not make function
calls to traceable functions when they are in the stopped state.

Commit ce4f06dcbb ("stop_machine: Touch_nmi_watchdog() after
MULTI_STOP_PREPARE") added calls to the watchdog touch functions from
the stopped CPUs and those functions lack notrace annotations.  This
leads to crashes when enabling/disabling ftrace on ARM kernels built
with the Thumb-2 instruction set.

Fix it by adding the necessary notrace annotations.

Fixes: ce4f06dcbb ("stop_machine: Touch_nmi_watchdog() after MULTI_STOP_PREPARE")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: oleg@redhat.com
Cc: tj@kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180821152507.18313-1-vincent.whitchurch@axis.com
2018-08-30 12:56:40 +02:00
Peter Zijlstra
be45bf5395 watchdog/softlockup: Fix cpu_stop_queue_work() double-queue bug
When scheduling is delayed for longer than the softlockup interrupt
period it is possible to double-queue the cpu_stop_work, causing list
corruption.

Cure this by adding a completion to track the cpu_stop_work's
progress.

Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Rong Chen <rong.a.chen@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cf57731b6 ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Link: http://lkml.kernel.org/r/20180713104208.GW2494@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-15 23:51:19 +02:00
Peter Zijlstra
9cf57731b6 watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work
Oleg suggested to replace the "watchdog/%u" threads with
cpu_stop_work. That removes one thread per CPU while at the same time
fixes softlockup vs SCHED_DEADLINE.

But more importantly, it does away with the single
smpboot_update_cpumask_percpu_thread() user, which allows
cleanups/shrinkage of the smpboot interface.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 09:20:43 +02:00
Ingo Molnar
8a103df440 Merge branch 'linus' into sched/core, to pick up fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-11-08 10:17:15 +01:00
Greg Kroah-Hartman
b24413180f License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-02 11:10:55 +01:00
Frederic Weisbecker
de201559df sched/isolation: Introduce housekeeping flags
Before we implement isolcpus under housekeeping, we need the isolation
features to be more finegrained. For example some people want NOHZ_FULL
without the full scheduler isolation, others want full scheduler
isolation without NOHZ_FULL.

So let's cut all these isolation features piecewise, at the risk of
overcutting it right now. We can still merge some flags later if they
always make sense together.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Link: http://lkml.kernel.org/r/1509072159-31808-9-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-27 09:55:29 +02:00
Frederic Weisbecker
13316b31fd sched/isolation, watchdog: Use housekeeping_cpumask() instead of ad-hoc version
While trying to disable the watchog on nohz_full CPUs, the watchdog
implements an ad-hoc version of housekeeping_cpumask(). Lets replace
those re-invented lines.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Link: http://lkml.kernel.org/r/1509072159-31808-3-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-27 09:55:25 +02:00
Frederic Weisbecker
7863406143 sched/isolation: Move housekeeping related code to its own file
The housekeeping code is currently tied to the NOHZ code. As we are
planning to make housekeeping independent from it, start with moving
the relevant code to its own file.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Link: http://lkml.kernel.org/r/1509072159-31808-2-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-27 09:55:24 +02:00
Thomas Gleixner
0b62bf862d watchdog/core: Put softlockup_threads_initialized under ifdef guard
The variable is unused when the softlockup detector is disabled in Kconfig.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2017-10-04 11:30:50 +02:00
Thomas Gleixner
5587185ddb watchdog/core: Rename some softlockup_* functions
The function names made sense up to the point where the watchdog
(re)configuration was unified to use softlockup_reconfigure_threads() for
all configuration purposes. But that includes scenarios which solely
configure the nmi watchdog.

Rename softlockup_reconfigure_threads() and softlockup_init_threads() so
the function names match the functionality.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Don Zickus <dzickus@redhat.com>
2017-10-04 10:53:54 +02:00
Thomas Gleixner
34ddaa3e5c powerpc/watchdog: Make use of watchdog_nmi_probe()
The rework of the core hotplug code triggers the WARN_ON in start_wd_cpu()
on powerpc because it is called multiple times for the boot CPU.

The first call is via:

  start_wd_on_cpu+0x80/0x2f0
  watchdog_nmi_reconfigure+0x124/0x170
  softlockup_reconfigure_threads+0x110/0x130
  lockup_detector_init+0xbc/0xe0
  kernel_init_freeable+0x18c/0x37c
  kernel_init+0x2c/0x160
  ret_from_kernel_thread+0x5c/0xbc

And then again via the CPU hotplug registration:

  start_wd_on_cpu+0x80/0x2f0
  cpuhp_invoke_callback+0x194/0x620
  cpuhp_thread_fun+0x7c/0x1b0
  smpboot_thread_fn+0x290/0x2a0
  kthread+0x168/0x1b0
  ret_from_kernel_thread+0x5c/0xbc

This can be avoided by setting up the cpu hotplug state with nocalls and
move the initialization to the watchdog_nmi_probe() function. That
initializes the hotplug callbacks without invoking the callback and the
following core initialization function then configures the watchdog for the
online CPUs (in this case CPU0) via softlockup_reconfigure_threads().

Reported-and-tested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
2017-10-04 10:53:54 +02:00
Thomas Gleixner
e31d6883f2 watchdog/core, powerpc: Lock cpus across reconfiguration
Instead of dropping the cpu hotplug lock after stopping NMI watchdog and
threads and reaquiring for restart, the code and the protection rules
become more obvious when holding cpu hotplug lock across the full
reconfiguration.

Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710022105570.2114@nanos
2017-10-04 10:53:54 +02:00
Thomas Gleixner
6b9dc4806b watchdog/core, powerpc: Replace watchdog_nmi_reconfigure()
The recent cleanup of the watchdog code split watchdog_nmi_reconfigure()
into two stages. One to stop the NMI and one to restart it after
reconfiguration. That was done by adding a boolean 'run' argument to the
code, which is functionally correct but not necessarily a piece of art.

Replace it by two explicit functions: watchdog_nmi_stop() and
watchdog_nmi_start().

Fixes: 6592ad2fcc ("watchdog/core, powerpc: Make watchdog_nmi_reconfigure() two stage")
Requested-by: Linus 'Nursing his pet-peeve' Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Thomas 'Mopping up garbage' Gleixner <tglx@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710021957480.2114@nanos
2017-10-04 10:53:53 +02:00
Thomas Gleixner
ab5fe3ff38 watchdog/hardlockup: Clean up hotplug locking mess
All watchdog thread related functions are delegated to the smpboot thread
infrastructure, which handles serialization against CPU hotplug correctly.

The sysctl interface is completely decoupled from anything which requires
CPU hotplug protection.

No need to protect the sysctl writes against cpu hotplug anymore. Remove it
and add the now required protection to the powerpc arch_nmi_watchdog
implementation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20170912194148.418497420@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:09 +02:00
Thomas Gleixner
146c9d0e9d watchdog/hardlockup/perf: Use new perf CPU enable mechanism
Get rid of the hodgepodge which tries to be smart about perf being
unavailable and error printout rate limiting.

That's all not required simply because this is never invoked when the perf
NMI watchdog is not functional.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194148.259651788@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:08 +02:00
Thomas Gleixner
a994a3147e watchdog/hardlockup/perf: Implement init time detection of perf
Use the init time detection of the perf NMI watchdog to determine whether
the perf NMI watchdog is functional. If not disable it permanentely. It
won't come back magically at runtime.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194148.099799541@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:08 +02:00
Thomas Gleixner
091549858e watchdog/core: Get rid of the racy update loop
Letting user space poke directly at variables which are used at run time is
stupid and causes a lot of race conditions and other issues.

Seperate the user variables and on change invoke the reconfiguration, which
then stops the watchdogs, reevaluates the new user value and restarts the
watchdogs with the new parameters.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.939985640@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:07 +02:00
Thomas Gleixner
6592ad2fcc watchdog/core, powerpc: Make watchdog_nmi_reconfigure() two stage
Both the perf reconfiguration and the powerpc watchdog_nmi_reconfigure()
need to be done in two steps.

     1) Stop all NMIs
     2) Read the new parameters and start NMIs

Right now watchdog_nmi_reconfigure() is a combination of both. To allow a
clean reconfiguration add a 'run' argument and split the functionality in
powerpc.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20170912194147.862865570@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:07 +02:00
Thomas Gleixner
7feeb9cd4f watchdog/sysctl: Clean up sysctl variable name space
Reflect that these variables are user interface related and remove the
whitespace damage in the sysctl table while at it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.783210221@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:07 +02:00
Thomas Gleixner
e8b62b2dd1 watchdog/core: Further simplify sysctl handling
Use a single function to update sysctl changes. This is not a high
frequency user space interface and it's root only.

Preparatory patch to cleanup the sysctl variable handling.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.549114957@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:06 +02:00
Thomas Gleixner
d57108d4f6 watchdog/core: Get rid of the thread teardown/setup dance
The lockup detector reconfiguration tears down all watchdog threads when
the watchdog is disabled and sets them up again when its enabled.

That's a pointless exercise. The watchdog threads are not consuming an
insane amount of resources, so it's enough to set them up at init time and
keep them in parked position when the watchdog is disabled and unpark them
when it is reenabled. The smpboot thread infrastructure takes care of
keeping the force parked threads in place even across cpu hotplug.

Aside of that the code implements the park/unpark facility of smp hotplug
threads on its own, which is even more pointless. We have functionality in
the smpboot thread code to do so.

Use the new thread management functions and get rid of the unholy mess.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.470370113@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:06 +02:00
Thomas Gleixner
2eb2527f84 watchdog/core: Create new thread handling infrastructure
The lockup detector reconfiguration tears down all watchdog threads when
the watchdog is disabled and sets them up again when its enabled.

That's a pointless exercise. The watchdog threads are not consuming an
insane amount of resources, so it's enough to set them up at init time and
keep them in parked position when the watchdog is disabled and unpark them
when it is reenabled. The smpboot thread infrastructure takes care of
keeping the force parked threads in place even across cpu hotplug.

Another horrible mechanism are the open coded park/unpark loops which are
used for reconfiguration of the watchdog. The smpboot infrastructure allows
exactly the same via smpboot_update_cpumask_thread_percpu(), which is cpu
hotplug safe. Using that instead of the open coded loops allows to get rid
of the hotplug locking mess in the watchdog code.

Implement a clean infrastructure which allows to replace the open coded
nonsense.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.377182587@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:06 +02:00
Thomas Gleixner
0d85923c7a smpboot/threads, watchdog/core: Avoid runtime allocation
smpboot_update_cpumask_threads_percpu() allocates a temporary cpumask at
runtime. This is suboptimal because the call site needs more code size for
proper error handling than a statically allocated temporary mask requires
data size.

Add static temporary cpumask. The function is globaly serialized, so no
further protection required.

Remove the half baken error handling in the watchdog code and get rid of
the export as there are no in tree modular users of that function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.297288838@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:06 +02:00
Thomas Gleixner
05ba3de74a watchdog/core: Split out cpumask write function
Split the write part of the cpumask proc handler out into a separate helper
to avoid deep indentation. This also reduces the patch complexity in the
following cleanups.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.218075991@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:06 +02:00
Thomas Gleixner
368a7e2ce8 watchdog/core: Clean up the #ifdef maze
The #ifdef maze in this file is horrible, group stuff at least a bit so one
can figure out what belongs to what.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.139629546@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:05 +02:00
Thomas Gleixner
2b9d7f233b watchdog/core: Clean up stub functions
Having stub functions which take a full page is not helping the
readablility of code.

Condense them and move the doubled #ifdef variant into the SYSFS section.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194147.045545271@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:05 +02:00
Thomas Gleixner
01f0a02701 watchdog/core: Remove the park_in_progress obfuscation
Commit:

  b94f51183b ("kernel/watchdog: prevent false hardlockup on overloaded system")

tries to fix the following issue:

proc_write()
   set_sample_period()    <--- New sample period becoms visible
			  <----- Broken starts
   proc_watchdog_update()
     watchdog_enable_all_cpus()		watchdog_hrtimer_fn()
     update_watchdog_all_cpus()		   restart_timer(sample_period)
        watchdog_park_threads()

					thread->park()
					  disable_nmi()
			  <----- Broken ends

The reason why this is broken is that the update of the watchdog threshold
becomes immediately effective and visible for the hrtimer function which
uses that value to rearm the timer. But the NMI/perf side still uses the
old value up to the point where it is disabled. If the rate has been
lowered then the NMI can run fast enough to 'detect' a hard lockup because
the timer has not fired due to the longer period.

The patch 'fixed' this by adding a variable:

proc_write()
   set_sample_period()
					<----- Broken starts
   proc_watchdog_update()
     watchdog_enable_all_cpus()		watchdog_hrtimer_fn()
     update_watchdog_all_cpus()		   restart_timer(sample_period)
         watchdog_park_threads()
	  park_in_progress = 1
					<----- Broken ends
				        nmi_watchdog()
					  if (park_in_progress)
					     return;

The only effect of this variable was to make the window where the breakage
can hit small enough that it was not longer observable in testing. From a
correctness point of view it is a pointless bandaid which merily papers
over the root cause: the unsychronized update of the variable.

Looking deeper into the related code pathes unearthed similar problems in
the watchdog_start()/stop() functions.

 watchdog_start()
	perf_nmi_event_start()
	hrtimer_start()

 watchdog_stop()
	hrtimer_cancel()
	perf_nmi_event_stop()

In both cases the call order is wrong because if the tasks gets preempted
or the VM gets scheduled out long enough after the first call, then there is
a chance that the next NMI will see a stale hrtimer interrupt count and
trigger a false positive hard lockup splat.

Get rid of park_in_progress so the code can be gradually deobfuscated and
pruned from several layers of duct tape papering over the root cause,
which has been either ignored or not understood at all.

Once this is removed the underlying problem will be fixed by rewriting the
proc interface to do a proper synchronized update.

Address the start/stop() ordering problem as well by reverting the call
order, so this part is at least correct now.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1709052038270.2393@nanos
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:05 +02:00
Thomas Gleixner
941154bd69 watchdog/hardlockup/perf: Prevent CPU hotplug deadlock
The following deadlock is possible in the watchdog hotplug code:

  cpus_write_lock()
    ...
      takedown_cpu()
        smpboot_park_threads()
          smpboot_park_thread()
            kthread_park()
              ->park() := watchdog_disable()
                watchdog_nmi_disable()
                  perf_event_release_kernel();
                    put_event()
                      _free_event()
                        ->destroy() := hw_perf_event_destroy()
                          x86_release_hardware()
                            release_ds_buffers()
                              get_online_cpus()

when a per cpu watchdog perf event is destroyed which drops the last
reference to the PMU hardware. The cleanup code there invokes
get_online_cpus() which instantly deadlocks because the hotplug percpu
rwsem is write locked.

To solve this add a deferring mechanism:

  cpus_write_lock()
			   kthread_park()
			    watchdog_nmi_disable(deferred)
			      perf_event_disable(event);
			      move_event_to_deferred(event);
			   ....
  cpus_write_unlock()
  cleaup_deferred_events()
    perf_event_release_kernel()

This is still properly serialized against concurrent hotplug via the
cpu_add_remove_lock, which is held by the task which initiated the hotplug
event.

This is also used to handle event destruction when the watchdog threads are
parked via other mechanisms than CPU hotplug.

Analyzed-by: Peter Zijlstra <peterz@infradead.org>

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194146.884469246@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:05 +02:00
Thomas Gleixner
20d853fd07 watchdog/hardlockup/perf: Remove broken self disable on failure
The self disabling feature is broken vs. CPU hotplug locking:

CPU 0			   CPU 1
cpus_write_lock();
 cpu_up(1)
   wait_for_completion()
			   ....
			   unpark_watchdog()
			   ->unpark()
			     perf_event_create() <- fails
			       watchdog_enable &= ~NMI_WATCHDOG;
			   ....
cpus_write_unlock();
			   CPU 2
cpus_write_lock()
 cpu_down(2)
   wait_for_completion()
			   wakeup(watchdog);
			     watchdog()
			     if (!(watchdog_enable & NMI_WATCHDOG))
				watchdog_nmi_disable()
				  perf_event_disable()
				  ....
				  cpus_read_lock();

			   stop_smpboot_threads()
			     park_watchdog();
			       wait_for_completion(watchdog->parked);

Result: End of hotplug and instantaneous full lockup of the machine.

There is a similar problem with disabling the watchdog via the user space
interface as the sysctl function fiddles with watchdog_enable directly.

It's very debatable whether this is required at all. If the watchdog works
nicely on N CPUs and it fails to enable on the N + 1 CPU either during
hotplug or because the user space interface disabled it via sysctl cpumask
and then some perf user grabbed the counter which is then unavailable for
the watchdog when the sysctl cpumask gets changed back.

There is no real justification for this.

One of the reasons WHY this is done is the utter stupidity of the init code
of the perf NMI watchdog. Instead of checking upfront at boot whether PERF
is available and functional at all, it just does this check at run time
over and over when user space fiddles with the sysctl. That's broken beyond
repair along with the idiotic error code dependent warn level printks and
the even more silly printk rate limiting.

If the init code checks whether perf works at boot time, then this mess can
be more or less avoided completely. Perf does not come magically into life
at runtime. Brain usage while coding is overrated.

Remove the cruft and add a temporary safe guard which gets removed later.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194146.806708429@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:04 +02:00
Thomas Gleixner
7a35582007 watchdog/core: Mark hardlockup_detector_disable() __init
The function is only used by the KVM init code. Mark it __init to prevent
creative abuse.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Link: http://lkml.kernel.org/r/20170912194146.727134632@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-14 11:41:04 +02:00