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b7fa30c9cc
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Peter Zijlstra b7fa30c9cc sched/fair: Fix post_init_entity_util_avg() serialization 
Chris Wilson reported a divide by 0 at:

 post_init_entity_util_avg():

 >    725	if (cfs_rq->avg.util_avg != 0) {
 >    726		sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
 > -> 727		sa->util_avg /= (cfs_rq->avg.load_avg + 1);
 >    728
 >    729		if (sa->util_avg > cap)
 >    730			sa->util_avg = cap;
 >    731	} else {

Which given the lack of serialization, and the code generated from
update_cfs_rq_load_avg() is entirely possible:

	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
		s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
		sa->load_avg = max_t(long, sa->load_avg - r, 0);
		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
		removed_load = 1;
	}

turns into:

  ffffffff81087064:       49 8b 85 98 00 00 00    mov    0x98(%r13),%rax
  ffffffff8108706b:       48 85 c0                test   %rax,%rax
  ffffffff8108706e:       74 40                   je     ffffffff810870b0
  ffffffff81087070:       4c 89 f8                mov    %r15,%rax
  ffffffff81087073:       49 87 85 98 00 00 00    xchg   %rax,0x98(%r13)
  ffffffff8108707a:       49 29 45 70             sub    %rax,0x70(%r13)
  ffffffff8108707e:       4c 89 f9                mov    %r15,%rcx
  ffffffff81087081:       bb 01 00 00 00          mov    $0x1,%ebx
  ffffffff81087086:       49 83 7d 70 00          cmpq   $0x0,0x70(%r13)
  ffffffff8108708b:       49 0f 49 4d 70          cmovns 0x70(%r13),%rcx

Which you'll note ends up with 'sa->load_avg - r' in memory at
ffffffff8108707a.

By calling post_init_entity_util_avg() under rq->lock we're sure to be
fully serialized against PELT updates and cannot observe intermediate
state like this.

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yuyang Du <yuyang.du@intel.com>
Cc: bsegall@google.com
Cc: morten.rasmussen@arm.com
Cc: pjt@google.com
Cc: steve.muckle@linaro.org
Fixes: 2b8c41daba ("sched/fair: Initiate a new task's util avg to a bounded value")
Link: http://lkml.kernel.org/r/20160609130750.GQ30909@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-06-14 10:58:34 +02:00
..
bpf Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-05-31 22:28:28 -07:00
configs
debug mm/init: Add 'rodata=off' boot cmdline parameter to disable read-only kernel mappings 2016-02-22 08:51:37 +01:00
events Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-06-10 11:15:41 -07:00
gcov gcov: disable for COMPILE_TEST 2016-05-10 17:12:49 +02:00
irq irqchip updates for 4.7-rc1: 2016-06-03 15:05:51 +02:00
livepatch Merge branches 'for-4.7/core', 'for-4.7/livepatching-doc' and 'for-4.7/livepatching-ppc64' into for-linus 2016-05-17 12:06:35 +02:00
locking locking/qspinlock: Fix spin_unlock_wait() some more 2016-06-08 14:29:08 +02:00
power PM / Hibernate: Call flush_icache_range() on pages restored in-place 2016-04-28 13:35:48 +01:00
printk printk/nmi: flush NMI messages on the system panic 2016-05-20 17:58:30 -07:00
rcu debugobjects: insulate non-fixup logic related to static obj from fixup callbacks 2016-05-19 19:12:14 -07:00
sched sched/fair: Fix post_init_entity_util_avg() serialization 2016-06-14 10:58:34 +02:00
time timer: Export destroy_hrtimer_on_stack() 2016-05-31 11:44:08 -07:00
trace bpf, trace: use READ_ONCE for retrieving file ptr 2016-06-07 14:48:03 -07:00
.gitignore certs: add .gitignore to stop git nagging about x509_certificate_list 2015-10-21 15:18:35 +01:00
acct.c
async.c async: export current_is_async() 2015-11-19 17:51:48 +01:00
audit_fsnotify.c wrappers for ->i_mutex access 2016-01-22 18:04:28 -05:00
audit_tree.c audit: cleanup prune_tree_thread 2016-04-04 09:46:47 -04:00
audit_watch.c don't bother with ->d_inode->i_sb - it's always equal to ->d_sb 2016-04-10 17:11:51 -04:00
audit.c Merge branch 'stable-4.7' of git://git.infradead.org/users/pcmoore/audit 2016-05-18 18:46:55 -07:00
audit.h security: Make inode argument of inode_getsecid non-const 2015-12-24 11:09:39 -05:00
auditfilter.c audit: Fix typo in comment 2016-02-08 11:25:39 -05:00
auditsc.c Merge branch 'stable-4.7' of git://git.infradead.org/users/pcmoore/audit 2016-05-18 18:46:55 -07:00
backtracetest.c
bounds.c
capability.c
cgroup_freezer.c cgroup: kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] and friends 2015-12-03 10:24:08 -05:00
cgroup_pids.c cgroup_pids: fix a typo. 2015-12-14 14:54:37 -05:00
cgroup.c cgroup: fix compile warning 2016-05-12 11:05:27 -04:00
compat.c
configs.c
context_tracking.c context_tracking: Switch to new static_branch API 2015-11-24 09:56:43 +01:00
cpu_pm.c kernel/cpu_pm: fix cpu_cluster_pm_exit comment 2015-09-03 02:42:20 +02:00
cpu.c sched/hotplug: Make activate() the last hotplug step 2016-05-06 14:58:25 +02:00
cpuset.c cpuset: use static key better and convert to new API 2016-05-19 19:12:14 -07:00
crash_dump.c
cred.c kmemcg: account certain kmem allocations to memcg 2016-01-14 16:00:49 -08:00
delayacct.c kmemcg: account certain kmem allocations to memcg 2016-01-14 16:00:49 -08:00
dma.c
elfcore.c
exec_domain.c
exit.c wait: allow sys_waitid() to accept __WNOTHREAD/__WCLONE/__WALL 2016-05-23 17:04:14 -07:00
extable.c kernel/extable.c: remove duplicated include 2015-09-10 13:29:01 -07:00
fork.c mm: oom_reaper: remove some bloat 2016-05-26 15:35:44 -07:00
freezer.c
futex_compat.c ptrace: use fsuid, fsgid, effective creds for fs access checks 2016-01-20 17:09:18 -08:00
futex.c futex: Calculate the futex key based on a tail page for file-based futexes 2016-06-08 19:23:54 +02:00
groups.c
hung_task.c kernel/hung_task.c: use timeout diff when timeout is updated 2016-03-22 15:36:02 -07:00
irq_work.c treewide: Remove old email address 2015-11-23 09:44:58 +01:00
jump_label.c treewide: Remove old email address 2015-11-23 09:44:58 +01:00
kallsyms.c kallsyms: add support for relative offsets in kallsyms address table 2016-03-15 16:55:16 -07:00
kcmp.c ptrace: use fsuid, fsgid, effective creds for fs access checks 2016-01-20 17:09:18 -08:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kcov.c kcov: don't profile branches in kcov 2016-04-28 19:34:04 -07:00
kexec_core.c s390/kexec: consolidate crash_map/unmap_reserved_pages() and arch_kexec_protect(unprotect)_crashkres() 2016-05-23 17:04:14 -07:00
kexec_file.c kexec: introduce a protection mechanism for the crashkernel reserved memory 2016-05-23 17:04:14 -07:00
kexec_internal.h kexec: move some memembers and definitions within the scope of CONFIG_KEXEC_FILE 2016-01-20 17:09:18 -08:00
kexec.c s390/kexec: consolidate crash_map/unmap_reserved_pages() and arch_kexec_protect(unprotect)_crashkres() 2016-05-23 17:04:14 -07:00
kmod.c kmod: don't run async usermode helper as a child of kworker thread 2015-10-23 17:55:10 +09:00
kprobes.c
ksysfs.c rcu: Remove TINY_RCU bloat from pointless boot parameters 2015-12-07 16:59:37 -08:00
kthread.c kernel/kthread.c:kthread_create_on_node(): clarify documentation 2015-09-04 16:54:41 -07:00
latencytop.c sched/debug: Make schedstats a runtime tunable that is disabled by default 2016-02-09 11:54:23 +01:00
Makefile ELF/MIPS build fix 2016-05-23 17:04:14 -07:00
membarrier.c sys_membarrier(): system-wide memory barrier (generic, x86) 2015-09-11 15:21:34 -07:00
memremap.c memremap: add arch specific hook for MEMREMAP_WB mappings 2016-04-04 10:26:41 +02:00
module_signing.c KEYS: Move the point of trust determination to __key_link() 2016-04-11 22:43:43 +01:00
module-internal.h
module.c module: preserve Elf information for livepatch modules 2016-04-01 15:00:10 +02:00
notifier.c Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-09-01 08:40:25 -07:00
nsproxy.c cgroup: introduce cgroup namespaces 2016-02-16 13:04:58 -05:00
padata.c kernel/padata.c: hide unused functions 2016-05-19 19:12:14 -07:00
panic.c printk/nmi: flush NMI messages on the system panic 2016-05-20 17:58:30 -07:00
params.c Nothing exciting, minor tweaks and cleanups. 2015-11-09 15:53:39 -08:00
pid_namespace.c
pid.c remove lots of IS_ERR_VALUE abuses 2016-05-27 15:26:11 -07:00
profile.c profile: hide unused functions when !CONFIG_PROC_FS 2016-03-22 15:36:02 -07:00
ptrace.c ptrace: change __ptrace_unlink() to clear ->ptrace under ->siglock 2016-03-22 15:36:02 -07:00
range.c
reboot.c kexec: split kexec_load syscall from kexec core code 2015-09-10 13:29:01 -07:00
relay.c kernel/relay.c: fix potential memory leak 2016-06-09 14:23:11 -07:00
resource.c /proc/iomem: only expose physical resource addresses to privileged users 2016-04-14 12:56:09 -07:00
seccomp.c Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-19 10:02:26 -07:00
signal.c kernel/signal.c: convert printk(KERN_<LEVEL> ...) to pr_<level>(...) 2016-05-23 17:04:14 -07:00
smp.c Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-03-15 13:50:29 -07:00
smpboot.c cpu/hotplug: Unpark smpboot threads from the state machine 2016-03-01 20:36:56 +01:00
smpboot.h cpu/hotplug: Create hotplug threads 2016-03-01 20:36:56 +01:00
softirq.c arch, ftrace: for KASAN put hard/soft IRQ entries into separate sections 2016-03-25 16:37:42 -07:00
stacktrace.c
stop_machine.c kernel/stop_machine.c: remove CONFIG_SMP dependencies 2016-01-16 11:17:24 -08:00
sys_ni.c vfs: add copy_file_range syscall and vfs helper 2015-12-01 14:00:53 -05:00
sys.c prctl: make PR_SET_THP_DISABLE wait for mmap_sem killable 2016-05-23 17:04:14 -07:00
sysctl_binary.c kernel/sysctl_binary.c: use generic UUID library 2016-05-20 17:58:30 -07:00
sysctl.c Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-05-25 17:05:40 -07:00
task_work.c task_work: remove fifo ordering guarantee 2015-09-05 13:46:58 -07:00
taskstats.c taskstats: use the libnl API to align nlattr on 64-bit 2016-04-23 20:13:25 -04:00
test_kprobes.c
torture.c rcutorture: Dump trace buffer upon shutdown 2016-04-21 13:47:04 -07:00
tracepoint.c kernel/...: convert pr_warning to pr_warn 2016-03-22 15:36:02 -07:00
tsacct.c time, acct: Drop irq save & restore from __acct_update_integrals() 2016-02-29 09:53:09 +01:00
uid16.c
up.c
user_namespace.c kernel/*: switch to memdup_user_nul() 2016-01-04 10:27:55 -05:00
user-return-notifier.c
user.c
utsname_sysctl.c
utsname.c
watchdog.c watchdog: don't run proc_watchdog_update if new value is same as old 2016-03-17 15:09:34 -07:00
workqueue_internal.h sched/core: Get rid of 'cpu' argument in wq_worker_sleeping() 2016-03-02 10:28:47 -05:00
workqueue.c debugobjects: insulate non-fixup logic related to static obj from fixup callbacks 2016-05-19 19:12:14 -07:00