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Michal Hocko 9809b18fcf watchdog: update watchdog_thresh properly 
watchdog_tresh controls how often nmi perf event counter checks per-cpu
hrtimer_interrupts counter and blows up if the counter hasn't changed
since the last check.  The counter is updated by per-cpu
watchdog_hrtimer hrtimer which is scheduled with 2/5 watchdog_thresh
period which guarantees that hrtimer is scheduled 2 times per the main
period.  Both hrtimer and perf event are started together when the
watchdog is enabled.

So far so good.  But...

But what happens when watchdog_thresh is updated from sysctl handler?

proc_dowatchdog will set a new sampling period and hrtimer callback
(watchdog_timer_fn) will use the new value in the next round.  The
problem, however, is that nobody tells the perf event that the sampling
period has changed so it is ticking with the period configured when it
has been set up.

This might result in an ear ripping dissonance between perf and hrtimer
parts if the watchdog_thresh is increased.  And even worse it might lead
to KABOOM if the watchdog is configured to panic on such a spurious
lockup.

This patch fixes the issue by updating both nmi perf even counter and
hrtimers if the threshold value has changed.

The nmi one is disabled and then reinitialized from scratch.  This has
an unpleasant side effect that the allocation of the new event might
fail theoretically so the hard lockup detector would be disabled for
such cpus.  On the other hand such a memory allocation failure is very
unlikely because the original event is deallocated right before.

It would be much nicer if we just changed perf event period but there
doesn't seem to be any API to do that right now.  It is also unfortunate
that perf_event_alloc uses GFP_KERNEL allocation unconditionally so we
cannot use on_each_cpu() and do the same thing from the per-cpu context.
The update from the current CPU should be safe because
perf_event_disable removes the event atomically before it clears the
per-cpu watchdog_ev so it cannot change anything under running handler
feet.

The hrtimer is simply restarted (thanks to Don Zickus who has pointed
this out) if it is queued because we cannot rely it will fire&adopt to
the new sampling period before a new nmi event triggers (when the
treshold is decreased).

[akpm@linux-foundation.org: the UP version of __smp_call_function_single ended up in the wrong place]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-09-24 17:00:25 -07:00
..
cpu idle: Enable interrupts in the weak arch_cpu_idle() implementation 2013-06-14 23:01:05 +02:00
debug kgdb/sysrq: fix inconstistent help message of sysrq key 2013-04-30 17:04:10 -07:00
events uprobes: Fix utask->depth accounting in handle_trampoline() 2013-09-12 08:00:55 +02:00
gcov kernel: replace strict_strto*() with kstrto*() 2013-09-12 15:38:03 -07:00
irq Remove GENERIC_HARDIRQ config option 2013-09-13 15:09:52 +02:00
power ACPI and power management fixes for 3.12-rc1 2013-09-12 11:22:45 -07:00
printk TTY/Serial driver patches for 3.12-rc1 2013-09-03 11:38:36 -07:00
sched Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-09-18 11:23:32 -05:00
time Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-09-18 11:24:49 -05:00
trace Not much changes for the 3.12 merge window. The major tracing changes 2013-09-09 14:42:15 -07:00
.gitignore kernel/hz.bc: ignore. 2013-04-22 07:09:06 -07:00
acct.c fs: Fix hang with BSD accounting on frozen filesystem 2013-05-04 14:57:58 -04:00
async.c async: rename and redefine async_func_ptr 2013-03-12 13:59:14 -07:00
audit.c audit: wait_for_auditd() should use TASK_UNINTERRUPTIBLE 2013-06-12 16:29:45 -07:00
audit.h audit: fix mq_open and mq_unlink to add the MQ root as a hidden parent audit_names record 2013-07-09 10:33:19 -07:00
audit_tree.c kernel/audit_tree.c:audit_add_tree_rule(): protect `rule' from kill_rules() 2013-06-12 16:29:46 -07:00
audit_watch.c
auditfilter.c audit: Fix decimal constant description 2013-07-09 10:33:19 -07:00
auditsc.c audit: fix mq_open and mq_unlink to add the MQ root as a hidden parent audit_names record 2013-07-09 10:33:19 -07:00
backtracetest.c
bounds.c
capability.c xfs: update for v3.12-rc1 2013-09-09 11:19:09 -07:00
cgroup.c Kill indirect include of file.h from eventfd.h, use fdget() in cgroup.c 2013-09-07 19:54:57 -04:00
cgroup_freezer.c cgroup: make css_for_each_descendant() and friends include the origin css in the iteration 2013-08-08 20:11:27 -04:00
compat.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2013-05-01 07:21:43 -07:00
configs.c proc: Supply PDE attribute setting accessor functions 2013-05-01 17:29:18 -04:00
context_tracking.c context_tracking: User/kernel broundary cross trace events 2013-08-14 17:14:48 +02:00
cpu.c ACPI / processor: Acquire writer lock to update CPU maps 2013-08-13 12:20:16 +02:00
cpu_pm.c
cpuset.c Merge branch 'for-3.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2013-09-03 18:25:03 -07:00
crash_dump.c
cred.c
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c ptrace: revert "Prepare to fix racy accesses on task breakpoints" 2013-07-09 10:33:26 -07:00
extable.c extable: skip sorting if the table is empty 2013-09-11 15:58:25 -07:00
fork.c Merge git://git.kvack.org/~bcrl/aio-next 2013-09-13 10:55:58 -07:00
freezer.c freezer: set PF_SUSPEND_TASK flag on tasks that call freeze_processes 2013-07-30 14:05:06 +02:00
futex.c futex: Use freezable blocking call 2013-06-25 23:11:19 +02:00
futex_compat.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal 2013-02-23 18:50:11 -08:00
groups.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
hrtimer.c kernel: delete __cpuinit usage from all core kernel files 2013-07-14 19:36:59 -04:00
hung_task.c hung_task debugging: Print more info when reporting the problem 2013-08-02 11:02:42 +02:00
irq_work.c Merge branch 'nohz/printk-v8' into irq/core 2013-02-05 00:48:46 +01:00
itimer.c
jump_label.c jump_label: Split jumplabel ratelimit 2013-08-09 07:53:54 -07:00
kallsyms.c kernel: kallsyms: memory override issue, need check destination buffer length 2013-04-15 15:17:26 +09:30
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks locking: Fix copy/paste errors of "ARCH_INLINE_*_UNLOCK_BH" 2013-05-28 08:50:00 +02:00
Kconfig.preempt
kexec.c kexec: remove unnecessary return 2013-09-11 15:59:10 -07:00
kmod.c usermodehelper: kill the sub_info->path[0] check 2013-07-03 16:08:02 -07:00
kprobes.c kprobes: allow to specify custom allocator for insn caches 2013-09-11 15:58:52 -07:00
ksysfs.c kernel: replace strict_strto*() with kstrto*() 2013-09-12 15:38:03 -07:00
kthread.c kthread: implement probe_kthread_data() 2013-04-30 17:04:02 -07:00
latencytop.c
lglock.c lglock: Update lockdep annotations to report recursive local locks 2013-07-12 13:51:19 +02:00
lockdep.c lockdep: remove task argument from debug_check_no_locks_held 2013-05-12 14:16:21 +02:00
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
Makefile Remove GENERIC_HARDIRQ config option 2013-09-13 15:09:52 +02:00
modsign_certificate.S CONFIG_SYMBOL_PREFIX: cleanup. 2013-03-15 15:09:43 +10:30
modsign_pubkey.c kernel/modsign_pubkey.c: fix init const for module signing code 2013-09-11 15:58:21 -07:00
module-internal.h
module.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-09-05 08:50:26 -07:00
module_signing.c
mutex-debug.c
mutex-debug.h
mutex.c Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-09-04 08:18:19 -07:00
mutex.h
notifier.c
nsproxy.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-09-07 14:35:32 -07:00
padata.c padata - Register hotcpu notifier after initialization 2013-08-29 14:37:59 +10:00
panic.c panic: call panic handlers before kmsg_dump 2013-09-11 15:59:30 -07:00
params.c kernel: replace strict_strto*() with kstrto*() 2013-09-12 15:38:03 -07:00
pid.c pidns: Fix hang in zap_pid_ns_processes by sending a potentially extra wakeup 2013-08-30 17:30:37 -07:00
pid_namespace.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-09-07 14:35:32 -07:00
posix-cpu-timers.c posix_timers: fix racy timer delta caching on task exit 2013-07-03 16:54:42 +02:00
posix-timers.c posix-timers: Remove unused variable 2013-04-18 12:51:19 +02:00
profile.c kernel: delete __cpuinit usage from all core kernel files 2013-07-14 19:36:59 -04:00
ptrace.c __ptrace_may_access() should not deny sub-threads 2013-09-11 15:59:01 -07:00
range.c range: Do not add new blank slot with add_range_with_merge 2013-06-18 11:32:10 -05:00
rcu.h rcu: Make call_rcu() leak callbacks for debug-object errors 2013-08-18 17:40:03 -07:00
rcupdate.c Not much changes for the 3.12 merge window. The major tracing changes 2013-09-09 14:42:15 -07:00
rcutiny.c rcu: Add const annotation to char * for RCU tracepoints and functions 2013-07-29 17:07:49 -04:00
rcutiny_plugin.h rcu: Add const annotation to char * for RCU tracepoints and functions 2013-07-29 17:07:49 -04:00
rcutorture.c rcu: Make rcutorture emit online failures if verbose 2013-08-20 11:38:45 -07:00
rcutree.c Merge branches 'doc.2013.08.19a', 'fixes.2013.08.20a', 'sysidle.2013.08.31a' and 'torture.2013.08.20a' into HEAD 2013-08-31 14:44:45 -07:00
rcutree.h nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU 2013-08-31 14:44:02 -07:00
rcutree_plugin.h nohz_full: Force RCU's grace-period kthreads onto timekeeping CPU 2013-08-31 14:44:02 -07:00
rcutree_trace.c rcutrace: single_open() leaks 2013-05-05 00:16:35 -04:00
reboot.c reboot: move arch/x86 reboot= handling to generic kernel 2013-07-09 10:33:29 -07:00
relay.c kernel: delete __cpuinit usage from all core kernel files 2013-07-14 19:36:59 -04:00
res_counter.c memcg: reduce function dereference 2013-09-12 15:38:02 -07:00
resource.c kernel/resource.c: remove the unneeded assignment in function __find_resource 2013-07-03 16:08:06 -07:00
rtmutex-debug.c sched/rt: Move rt specific bits into new header file 2013-02-07 20:51:08 +01:00
rtmutex-debug.h
rtmutex-tester.c locking/rtmutex/tester: Set correct permissions on sysfs files 2013-04-10 14:48:37 +02:00
rtmutex.c rtmutex: Document rt_mutex_adjust_prio_chain() 2013-05-28 09:23:52 +02:00
rtmutex.h
rtmutex_common.h
rwsem.c Revert "rw_semaphore: remove up/down_read_non_owner" 2013-03-23 15:53:52 -07:00
seccomp.c seccomp: allow BPF_XOR based ALU instructions. 2013-03-26 11:07:19 +11:00
semaphore.c semaphore: use `bool' type for semaphore_waiter's up 2013-04-30 17:04:08 -07:00
signal.c kernel-wide: fix missing validations on __get/__put/__copy_to/__copy_from_user() 2013-09-11 15:58:18 -07:00
smp.c kernel/smp.c: quit unconditionally enabling irqs in on_each_cpu_mask(). 2013-09-11 15:58:25 -07:00
smpboot.c kernel: delete __cpuinit usage from all core kernel files 2013-07-14 19:36:59 -04:00
smpboot.h
softirq.c Remove GENERIC_HARDIRQ config option 2013-09-13 15:09:52 +02:00
spinlock.c kernel/spinlock.c: add default arch_*_relax definitions for GENERIC_LOCKBREAK 2013-09-11 15:58:21 -07:00
srcu.c srcu: use ACCESS_ONCE() to access sp->completed in srcu_read_lock() 2013-02-07 15:19:36 -08:00
stacktrace.c
stop_machine.c stop_machine: Mark per cpu stopper enabled early 2013-02-26 22:25:17 +01:00
sys.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
sys_ni.c unify compat fanotify_mark(2), switch to COMPAT_SYSCALL_DEFINE 2013-05-09 13:46:38 -04:00
sysctl.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-09-12 15:01:38 -07:00
sysctl_binary.c kernel: remove unnecessary head file 2013-06-26 18:01:46 +09:00
task_work.c task_work: documentation 2013-09-11 15:58:27 -07:00
taskstats.c
test_kprobes.c kernel/: rename random32() to prandom_u32() 2013-04-29 18:28:42 -07:00
time.c sched: Rename sched.c as sched/core.c in comments and Documentation 2013-06-19 12:58:42 +02:00
timeconst.bc kernel: Replace timeconst.pl with a bc script 2013-02-16 23:17:25 +01:00
timer.c kernel: delete __cpuinit usage from all core kernel files 2013-07-14 19:36:59 -04:00
tracepoint.c Tracing updates for Linux 3.10 2013-04-29 13:55:38 -07:00
tsacct.c
uid16.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
up.c smp.h: move !SMP version of on_each_cpu() out-of-line 2013-09-11 15:58:25 -07:00
user-return-notifier.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
user.c userns: Better restrictions on when proc and sysfs can be mounted 2013-08-26 19:17:03 -07:00
user_namespace.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-09-07 14:35:32 -07:00
utsname.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
utsname_sysctl.c kernel/utsname_sysctl.c: put get/get_uts() into CONFIG_PROC_SYSCTL code block 2013-02-27 19:10:22 -08:00
wait.c kernel: fix new kernel-doc warning in wait.c 2013-08-19 09:08:54 -07:00
watchdog.c watchdog: update watchdog_thresh properly 2013-09-24 17:00:25 -07:00
workqueue.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2013-09-06 09:36:28 -07:00
workqueue_internal.h sched: Rename sched.c as sched/core.c in comments and Documentation 2013-06-19 12:58:42 +02:00