If kthread_park() returns an error, watchdog_park_threads() should not
blindly 'roll back' the already parked threads to the unparked state.
Instead leave it up to the callers to handle such errors appropriately in
their context.  For example, it is redundant to unpark the threads if the
lockup detectors will soon be disabled by the callers anyway.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lockup_detector_suspend() now handles errors from watchdog_park_threads().
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

update_watchdog_all_cpus() now passes errors from watchdog_park_threads()
up to functions in the call chain.  This allows watchdog_enable_all_cpus()
and proc_watchdog_update() to handle such errors too.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Move watchdog_disable_all_cpus() outside of the ifdef so that it is
available if CONFIG_SYSCTL is not defined.  This is preparation for
"watchdog: implement error handling in update_watchdog_all_cpus() and
callers".
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The original watchdog_park_threads() function that was introduced by
commit 81a4beef ("watchdog: introduce watchdog_park_threads() and
watchdog_unpark_threads()") takes a very simple approach to handle
errors returned by kthread_park(): It attempts to roll back all watchdog
threads to the unparked state.  However, this may be undesired behaviour
from the perspective of the caller which may want to handle errors as
appropriate in its specific context.  Currently, there are two possible
call chains:

- watchdog suspend/resume interface

    lockup_detector_suspend
      watchdog_park_threads

- write to parameters in /proc/sys/kernel

    proc_watchdog_update
      watchdog_enable_all_cpus
        update_watchdog_all_cpus
          watchdog_park_threads

Instead of 'blindly' attempting to unpark the watchdog threads if a
kthread_park() call fails, the new approach is to disable the lockup
detectors in the above call chains.  Failure becomes visible to the user
as follows:

- error messages from lockup_detector_suspend()
                   or watchdog_enable_all_cpus()

- the state that can be read from /proc/sys/kernel/watchdog_enabled

- the 'write' system call in the latter call chain returns an error

I did not experience kthread_park() failures in practice, I used some
instrumentation to fake error returns from kthread_park() in order to test
the patches.

This patch (of 5):

Restore the previous value of watchdog_thresh _and_ sample_period if
proc_watchdog_update() returns an error.  The variables must be consistent
to avoid false positives of the lockup detectors.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Make is_hardlockup return bool to improve readability due to this
particular function only using either one or zero as its return value.

No functional change.
Signed-off-by: NYaowei Bai <bywxiaobai@163.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Rename watchdog_suspend() to lockup_detector_suspend() and
watchdog_resume() to lockup_detector_resume() to avoid confusion with the
watchdog subsystem and to be consistent with the existing name
lockup_detector_init().

Also provide comment blocks to explain the watchdog_running and
watchdog_suspended variables and their relationship.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Stephane Eranian <eranian@google.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Remove watchdog_nmi_disable_all() and watchdog_nmi_enable_all() since
these functions are no longer needed.  If a subsystem has a need to
deactivate the watchdog temporarily, it should utilize the
watchdog_suspend() and watchdog_resume() functions.

[akpm@linux-foundation.org: fix build with CONFIG_LOCKUP_DETECTOR=m]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Stephane Eranian <eranian@google.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Remove update_watchdog() and restart_watchdog_hrtimer() since these
functions are no longer needed.  Changes of parameters such as the sample
period are honored at the time when the watchdog threads are being
unparked.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Stephane Eranian <eranian@google.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This interface can be utilized to deactivate the hard and soft lockup
detector temporarily.  Callers are expected to minimize the duration of
deactivation.  Multiple deactivations are allowed to occur in parallel but
should be rare in practice.

[akpm@linux-foundation.org: remove unneeded static initialization]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Stephane Eranian <eranian@google.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Originally watchdog_nmi_enable(cpu) and watchdog_nmi_disable(cpu) were
only called in watchdog thread context.  However, the following commits
utilize these functions outside of watchdog thread context too.

  commit 9809b18f
  Author: Michal Hocko <mhocko@suse.cz>
  Date:   Tue Sep 24 15:27:30 2013 -0700

      watchdog: update watchdog_thresh properly

  commit b3738d29
  Author: Stephane Eranian <eranian@google.com>
  Date:   Mon Nov 17 20:07:03 2014 +0100

      watchdog: Add watchdog enable/disable all functions

Hence, it is now possible that these functions execute concurrently with
the same 'cpu' argument.  This concurrency is problematic because per-cpu
'watchdog_ev' can be accessed/modified without adequate synchronization.

The patch series aims to address the above problem.  However, instead of
introducing locks to protect per-cpu 'watchdog_ev' a different approach is
taken: Invoke these functions by parking and unparking the watchdog
threads (to ensure they are always called in watchdog thread context).

  static struct smp_hotplug_thread watchdog_threads = {
           ...
          .park   = watchdog_disable, // calls watchdog_nmi_disable()
          .unpark = watchdog_enable,  // calls watchdog_nmi_enable()
  };

Both previously mentioned commits call these functions in a similar way
and thus in principle contain some duplicate code.  The patch series also
avoids this duplication by providing a commonly usable mechanism.

- Patch 1/4 introduces the watchdog_{park|unpark}_threads functions that
  park/unpark all watchdog threads specified in 'watchdog_cpumask'. They
  are intended to be called inside of kernel/watchdog.c only.

- Patch 2/4 introduces the watchdog_{suspend|resume} functions which can
  be utilized by external callers to deactivate the hard and soft lockup
  detector temporarily.

- Patch 3/4 utilizes watchdog_{park|unpark}_threads to replace some code
  that was introduced by commit 9809b18f.

- Patch 4/4 utilizes watchdog_{suspend|resume} to replace some code that
  was introduced by commit b3738d29.

A few corner cases should be mentioned here for completeness.

- kthread_park() of watchdog/N could hang if cpu N is already locked up.
  However, if watchdog is enabled the lockup will be detected anyway.

- kthread_unpark() of watchdog/N could hang if cpu N got locked up after
  kthread_park(). The occurrence of this scenario should be _very_ rare
  in practice, in particular because it is not expected that temporary
  deactivation will happen frequently, and if it happens at all it is
  expected that the duration of deactivation will be short.

This patch (of 4): introduce watchdog_park_threads() and watchdog_unpark_threads()

These functions are intended to be used only from inside kernel/watchdog.c
to park/unpark all watchdog threads that are specified in
watchdog_cpumask.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Stephane Eranian <eranian@google.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The kernel's NMI watchdog has nothing to do with the watchdog subsystem.
Its header declarations should be in linux/nmi.h, not linux/watchdog.h.

The code provided two sets of dummy functions if HARDLOCKUP_DETECTOR is
not configured, one in the include file and one in kernel/watchdog.c.
Remove the dummy functions from kernel/watchdog.c and use those from the
include file.
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Cc: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Don Zickus <dzickus@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

housekeeping_mask gathers all the CPUs that aren't part of the nohz_full
set.  This is exactly what we want the watchdog to be affine to without
the need to use complicated cpumask operations.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: NChris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It makes the registration cheaper and simpler for the smpboot per-cpu
kthread users that don't need to always update the cpumask after threads
creation.

[sfr@canb.auug.org.au: fix for allow passing the cpumask on per-cpu thread registration]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: NChris Metcalf <cmetcalf@ezchip.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Change the default behavior of watchdog so it only runs on the
housekeeping cores when nohz_full is enabled at build and boot time.
Allow modifying the set of cores the watchdog is currently running on
with a new kernel.watchdog_cpumask sysctl.

In the current system, the watchdog subsystem runs a periodic timer that
schedules the watchdog kthread to run.  However, nohz_full cores are
designed to allow userspace application code running on those cores to
have 100% access to the CPU.  So the watchdog system prevents the
nohz_full application code from being able to run the way it wants to,
thus the motivation to suppress the watchdog on nohz_full cores, which
this patchset provides by default.

However, if we disable the watchdog globally, then the housekeeping
cores can't benefit from the watchdog functionality.  So we allow
disabling it only on some cores.  See Documentation/lockup-watchdogs.txt
for more information.

[jhubbard@nvidia.com: fix a watchdog crash in some configurations]
Signed-off-by: NChris Metcalf <cmetcalf@ezchip.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NJohn Hubbard <jhubbard@nvidia.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit ab992dc3 ("watchdog: Fix merge 'conflict'") has introduced an
obvious deadlock because of a typo.  watchdog_proc_mutex should be
unlocked on exit.

Thanks to Miroslav Benes who was staring at the code with me and noticed
this.
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Duh-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Two watchdog changes that came through different trees had a non
conflicting conflict, that is, one changed the semantics of a variable
but no actual code conflict happened. So the merge appeared fine, but
the resulting code did not behave as expected.

Commit 195daf66 ("watchdog: enable the new user interface of the
watchdog mechanism") changes the semantics of watchdog_user_enabled,
which thereafter is only used by the functions introduced by
b3738d29 ("watchdog: Add watchdog enable/disable all functions").

There further appears to be a distinct lack of serialization between
setting and using watchdog_enabled, so perhaps we should wrap the
{en,dis}able_all() things in watchdog_proc_mutex.

This patch fixes a s2r failure reported by Michal; which I cannot
readily explain. But this does make the code internally consistent
again.
Reported-and-tested-by: NMichal Hocko <mhocko@suse.cz>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Have kvm_guest_init() use hardlockup_detector_disable() instead of
watchdog_enable_hardlockup_detector(false).

Remove the watchdog_hardlockup_detector_is_enabled() and the
watchdog_enable_hardlockup_detector() function which are no longer needed.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Rename the update_timers*() functions to update_watchdog*().

Remove the boolean argument from watchdog_enable_all_cpus() because
update_watchdog_all_cpus() is now a generic function to change the run
state of the lockup detectors and to have the lockup detectors use a new
sample period.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

With the current user interface of the watchdog mechanism it is only
possible to disable or enable both lockup detectors at the same time.
This series introduces new kernel parameters and changes the semantics of
some existing kernel parameters, so that the hard lockup detector and the
soft lockup detector can be disabled or enabled individually.  With this
series applied, the user interface is as follows.

- parameters in /proc/sys/kernel

  . soft_watchdog
    This is a new parameter to control and examine the run state of
    the soft lockup detector.

  . nmi_watchdog
    The semantics of this parameter have changed. It can now be used
    to control and examine the run state of the hard lockup detector.

  . watchdog
    This parameter is still available to control the run state of both
    lockup detectors at the same time. If this parameter is examined,
    it shows the logical OR of soft_watchdog and nmi_watchdog.

  . watchdog_thresh
    The semantics of this parameter are not affected by the patch.

- kernel command line parameters

  . nosoftlockup
    The semantics of this parameter have changed. It can now be used
    to disable the soft lockup detector at boot time.

  . nmi_watchdog=0 or nmi_watchdog=1
    Disable or enable the hard lockup detector at boot time. The patch
    introduces '=1' as a new option.

  . nowatchdog
    The semantics of this parameter are not affected by the patch. It
    is still available to disable both lockup detectors at boot time.

Also, remove the proc_dowatchdog() function which is no longer needed.

[dzickus@redhat.com: wrote changelog]
[dzickus@redhat.com: update documentation for kernel params and sysctl]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If watchdog_nmi_enable() fails to set up the hardware perf event of one
CPU, the entire hard lockup detector is deemed unreliable.  Hence, disable
the hard lockup detector and shut down the hardware perf events on all
CPUs.

[dzickus@redhat.com: update comments to explain some code]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Separate handlers for each watchdog parameter in /proc/sys/kernel replace
the proc_dowatchdog() function.  Three of those handlers merely call
proc_watchdog_common() with one different argument.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Three of four handlers for the watchdog parameters in /proc/sys/kernel
essentially have to do the same thing.

  if the parameter is being read {
    return the state of the corresponding bit(s) in 'watchdog_enabled'
  } else {
    set/clear the state of the corresponding bit(s) in 'watchdog_enabled'
    update the run state of the lockup detector(s)
  }

Hence, introduce a common function that can be called by those handlers.
The callers pass a 'bit mask' to this function to indicate which bit(s)
should be set/cleared in 'watchdog_enabled'.

This function handles an uncommon race with watchdog_nmi_enable() where a
concurrent update of 'watchdog_enabled' is possible.  We use 'cmpxchg' to
detect the concurrency.  [This avoids introducing a new spinlock or a
mutex to synchronize updates of 'watchdog_enabled'.  Using the same lock
or mutex in watchdog thread context and in system call context needs to be
considered carefully because it can make the code prone to deadlock
situations in connection with parking/unparking the watchdog threads.]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This series removes proc_dowatchdog().  Since multiple new functions need
the 'watchdog_proc_mutex' to serialize access to the watchdog parameters
in /proc/sys/kernel, move the mutex outside of any function.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This series introduces a separate handler for each watchdog parameter in
/proc/sys/kernel.  The separate handlers need a common function that they
can call to update the run state of the lockup detectors, or to have the
lockup detectors use a new sample period.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The hardlockup and softockup had always been tied together.  Due to the
request of KVM folks, they had a need to have one enabled but not the
other.  Internally rework the code to split things apart more cleanly.

There is a bunch of churn here, but the end result should be code that
should be easier to maintain and fix without knowing the internals of what
is going on.

This patch (of 9):

Introduce new definitions and variables to separate the user interface in
/proc/sys/kernel from the internal run state of the lockup detectors.  The
internal run state is represented by two bits in a new variable that is
named 'watchdog_enabled'.  This helps simplify the code, for example:

- In order to check if any of the two lockup detectors is enabled,
  it is sufficient to check if 'watchdog_enabled' is not zero.

- In order to enable/disable one or both lockup detectors,
  it is sufficient to set/clear one or both bits in 'watchdog_enabled'.

- Concurrent updates of 'watchdog_enabled' need not be synchronized via
  a spinlock or a mutex. Updates can either be atomic or concurrency can
  be detected by using 'cmpxchg'.
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch adds two new functions to enable/disable
the watchdog across all CPUs.

This will be used by the HT PMU bug workaround code to
disable/enable the NMI watchdog across quirk enablement.
Signed-off-by: NStephane Eranian <eranian@google.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: bp@alien8.de
Cc: jolsa@redhat.com
Cc: kan.liang@intel.com
Cc: maria.n.dimakopoulou@gmail.com
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1416251225-17721-12-git-send-email-eranian@google.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

When the hypervisor pauses a virtualised kernel the kernel will observe a
jump in timebase, this can cause spurious messages from the softlockup
detector.

Whilst these messages are harmless, they are accompanied with a stack
trace which causes undue concern and more problematically the stack trace
in the guest has nothing to do with the observed problem and can only be
misleading.

Futhermore, on POWER8 this is completely avoidable with the introduction
of the Virtual Time Base (VTB) register.

This patch (of 2):

This permits the use of arch specific clocks for which virtualised kernels
can use their notion of 'running' time, not the elpased wall time which
will include host execution time.
Signed-off-by: NCyril Bur <cyrilbur@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Jones <drjones@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: chai wen <chaiw.fnst@cn.fujitsu.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Ben Zhang <benzh@chromium.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In some cases we don't want hard lockup detection enabled by default.
An example is when running as a guest.  Introduce

  watchdog_enable_hardlockup_detector(bool)

allowing those cases to disable hard lockup detection.  This must be
executed early by the boot processor from e.g.  smp_prepare_boot_cpu, in
order to allow kernel command line arguments to override it, as well as
to avoid hard lockup detection being enabled before we've had a chance
to indicate that it's unwanted.  In summary,

  initial boot:					default=enabled
  smp_prepare_boot_cpu
    watchdog_enable_hardlockup_detector(false):	default=disabled
  cmdline has 'nmi_watchdog=1':			default=enabled

The running kernel still has the ability to enable/disable at any time
with /proc/sys/kernel/nmi_watchdog us usual.  However even when the
default has been overridden /proc/sys/kernel/nmi_watchdog will initially
show '1'.  To truly turn it on one must disable/enable it, i.e.

  echo 0 > /proc/sys/kernel/nmi_watchdog
  echo 1 > /proc/sys/kernel/nmi_watchdog

This patch will be immediately useful for KVM with the next patch of this
series.  Other hypervisor guest types may find it useful as well.

[akpm@linux-foundation.org: fix build]
[dzickus@redhat.com: fix compile issues on sparc]
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

For now, soft lockup detector warns once for each case of process
softlockup.  But the thread 'watchdog/n' may not always get the cpu at the
time slot between the task switch of two processes hogging that cpu to
reset soft_watchdog_warn.

An example would be two processes hogging the cpu.  Process A causes the
softlockup warning and is killed manually by a user.  Process B
immediately becomes the new process hogging the cpu preventing the
softlockup code from resetting the soft_watchdog_warn variable.

This case is a false negative of "warn only once for a process", as there
may be a different process that is going to hog the cpu.  Resolve this by
saving/checking the task pointer of the hogging process and use that to
reset soft_watchdog_warn too.

[dzickus@redhat.com: update comment]
Signed-off-by: Nchai wen <chaiw.fnst@cn.fujitsu.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Most of these are the uses of &__raw_get_cpu_var for address calculation.

touch_softlockup_watchdog_sync() uses __raw_get_cpu_var to write to
per cpu variables. Use __this_cpu_write instead.

Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: linux-watchdog@vger.kernel.org
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

This patch avoids printing the message 'enabled on all CPUs,
...' multiple times. For example, the issue can occur in the
following scenario:

1) watchdog_nmi_enable() fails to enable PMU counters and sets
   cpu0_err.

2) 'echo [0|1] > /proc/sys/kernel/nmi_watchdog' is executed to
   disable and re-enable the watchdog mechanism 'on the fly'.

3) If watchdog_nmi_enable() succeeds to enable PMU counters,
   each CPU will print the message because step1 left behind a
   non-zero cpu0_err.

   if (!IS_ERR(event)) {
       if (cpu == 0 || cpu0_err)
           pr_info("enabled on all CPUs, ...")

The patch avoids this by clearing cpu0_err in watchdog_nmi_disable().
Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: pbonzini@redhat.com
Link: http://lkml.kernel.org/r/1407768567-171794-4-git-send-email-dzickus@redhat.com
[ Applied small cleanups. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: Nchai wen <chaiw.fnst@cn.fujitsu.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: pbonzini@redhat.com
Link: http://lkml.kernel.org/r/1407768567-171794-2-git-send-email-dzickus@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

This taint flag will be set if the system has ever entered a softlockup
state.  Similar to TAINT_WARN it is useful to know whether or not the
system has been in a softlockup state when debugging.

[akpm@linux-foundation.org: apply the taint before calling panic()]
Signed-off-by: NJosh Hunt <johunt@akamai.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Replace some obsolete functions.
Signed-off-by: NFabian Frederick <fabf@skynet.be>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A 'softlockup' is defined as a bug that causes the kernel to loop in
kernel mode for more than a predefined period to time, without giving
other tasks a chance to run.

Currently, upon detection of this condition by the per-cpu watchdog
task, debug information (including a stack trace) is sent to the system
log.

On some occasions, we have observed that the "victim" rather than the
actual "culprit" (i.e.  the owner/holder of the contended resource) is
reported to the user.  Often this information has proven to be
insufficient to assist debugging efforts.

To avoid loss of useful debug information, for architectures which
support NMI, this patch makes it possible to improve soft lockup
reporting.  This is accomplished by issuing an NMI to each cpu to obtain
a stack trace.

If NMI is not supported we just revert back to the old method.  A sysctl
and boot-time parameter is available to toggle this feature.

[dzickus@redhat.com: add CONFIG_SMP in certain areas]
[akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations]
[mq@suse.cz: fix warning]
Signed-off-by: NAaron Tomlin <atomlin@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Mateusz Guzik <mguzik@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: NJan Moskyto Matejka <mq@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Peter Wu noticed the following splat on his machine when updating
/proc/sys/kernel/watchdog_thresh:

  BUG: sleeping function called from invalid context at mm/slub.c:965
  in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: init
  3 locks held by init/1:
   #0:  (sb_writers#3){.+.+.+}, at: [<ffffffff8117b663>] vfs_write+0x143/0x180
   #1:  (watchdog_proc_mutex){+.+.+.}, at: [<ffffffff810e02d3>] proc_dowatchdog+0x33/0x110
   #2:  (cpu_hotplug.lock){.+.+.+}, at: [<ffffffff810589c2>] get_online_cpus+0x32/0x80
  Preemption disabled at:[<ffffffff810e0384>] proc_dowatchdog+0xe4/0x110

  CPU: 0 PID: 1 Comm: init Not tainted 3.16.0-rc1-testing #34
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
  Call Trace:
    dump_stack+0x4e/0x7a
    __might_sleep+0x11d/0x190
    kmem_cache_alloc_trace+0x4e/0x1e0
    perf_event_alloc+0x55/0x440
    perf_event_create_kernel_counter+0x26/0xe0
    watchdog_nmi_enable+0x75/0x140
    update_timers_all_cpus+0x53/0xa0
    proc_dowatchdog+0xe4/0x110
    proc_sys_call_handler+0xb3/0xc0
    proc_sys_write+0x14/0x20
    vfs_write+0xad/0x180
    SyS_write+0x49/0xb0
    system_call_fastpath+0x16/0x1b
  NMI watchdog: disabled (cpu0): hardware events not enabled

What happened is after updating the watchdog_thresh, the lockup detector
is restarted to utilize the new value.  Part of this process involved
disabling preemption.  Once preemption was disabled, perf tried to
allocate a new event (as part of the restart).  This caused the above
BUG_ON as you can't sleep with preemption disabled.

The preemption restriction seemed agressive as we are not doing anything
on that particular cpu, but with all the online cpus (which are
protected by the get_online_cpus lock).  Remove the restriction and the
BUG_ON goes away.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reported-by: NPeter Wu <peter@lekensteyn.nl>
Tested-by: NPeter Wu <peter@lekensteyn.nl>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>		[3.13+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Fix:

  BUG: using __this_cpu_write() in preemptible [00000000] code: systemd-udevd/497
  caller is __this_cpu_preempt_check+0x13/0x20
  CPU: 3 PID: 497 Comm: systemd-udevd Tainted: G        W     3.15.0-rc1 #9
  Hardware name: Hewlett-Packard HP EliteBook 8470p/179B, BIOS 68ICF Ver. F.02 04/27/2012
  Call Trace:
    check_preemption_disabled+0xe1/0xf0
    __this_cpu_preempt_check+0x13/0x20
    touch_nmi_watchdog+0x28/0x40
Reported-by: NLuis Henriques <luis.henriques@canonical.com>
Tested-by: NLuis Henriques <luis.henriques@canonical.com>
Cc: Eric Piel <eric.piel@tremplin-utc.net>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Lv Zheng <lv.zheng@intel.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

I ran into a scenario where while one cpu was stuck and should have
panic'd because of the NMI watchdog, it didn't.  The reason was another
cpu was spewing stack dumps on to the console.  Upon investigation, I
noticed that when writing to the console and also when dumping the
stack, the watchdog is touched.

This causes all the cpus to reset their NMI watchdog flags and the
'stuck' cpu just spins forever.

This change causes the semantics of touch_nmi_watchdog to be changed
slightly.  Previously, I accidentally changed the semantics and we
noticed there was a codepath in which touch_nmi_watchdog could be
touched from a preemtible area.  That caused a BUG() to happen when
CONFIG_DEBUG_PREEMPT was enabled.  I believe it was the acpi code.

My attempt here re-introduces the change to have the
touch_nmi_watchdog() code only touch the local cpu instead of all of the
cpus.  But instead of using __get_cpu_var(), I use the
__raw_get_cpu_var() version.

This avoids the preemption problem.  However my reasoning wasn't because
I was trying to be lazy.  Instead I rationalized it as, well if
preemption is enabled then interrupts should be enabled to and the NMI
watchdog will have no reason to trigger.  So it won't matter if the
wrong cpu is touched because the percpu interrupt counters the NMI
watchdog uses should still be incrementing.

Don said:

: I'm ok with this patch, though it does alter the behaviour of how
: touch_nmi_watchdog works.  For the most part I don't think most callers
: need to touch all of the watchdogs (on each cpu).  Perhaps a corner case
: will pop up (the scheduler??  to mimic touch_all_softlockup_watchdogs() ).
:
: But this does address an issue where if a system is locked up and one cpu
: is spewing out useful debug messages (or error messages), the hard lockup
: will fail to go off.  We have seen this on RHEL also.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NBen Zhang <benzh@chromium.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In order to remotely restart the watchdog hrtimer, update_timers()
allocates a csd on the stack and pass it to __smp_call_function_single().

There is no partcular need, however, for a specific csd here. Lets
simplify that a little by calling smp_call_function_single()
which can already take care of the csd allocation by itself.
Acked-by: NDon Zickus <dzickus@redhat.com>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>