The handler functions for watchdog parameters in /proc/sys/kernel do not
protect themselves against races with CPU hotplug. Hence, theoretically
it is possible that a new watchdog thread is started on a hotplugged CPU
while a parameter is being modified, and the thread could thus use a
parameter value that is 'in transition'.
For example, if 'watchdog_thresh' is being set to zero (note: this
disables the lockup detectors) the thread would erroneously use the value
zero as the sample period.
To avoid such races and to keep the /proc handler code consistent,
call
{get|put}_online_cpus() in proc_watchdog_common()
{get|put}_online_cpus() in proc_watchdog_thresh()
{get|put}_online_cpus() in proc_watchdog_cpumask()
Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The lockup detector suspend/resume interface that was introduced by
commit 8c073d27d7 ("watchdog: introduce watchdog_suspend() and
watchdog_resume()") does not protect itself against races with CPU
hotplug. Hence, theoretically it is possible that a new watchdog thread
is started on a hotplugged CPU while the lockup detector is suspended,
and the thread could thus interfere unexpectedly with the code that
requested to suspend the lockup detector.
Avoid the race by calling
get_online_cpus() in lockup_detector_suspend()
put_online_cpus() in lockup_detector_resume()
Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The only way to enable a hardlockup to panic the machine is to set
'nmi_watchdog=panic' on the kernel command line.
This makes it awkward for end users and folks who want to run automate
tests (like myself).
Mimic the softlockup_panic knob and create a /proc/sys/kernel/hardlockup_panic
knob.
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In many cases of hardlockup reports, it's actually not possible to know
why it triggered, because the CPU that got stuck is usually waiting on a
resource (with IRQs disabled) in posession of some other CPU is holding.
IOW, we are often looking at the stacktrace of the victim and not the
actual offender.
Introduce sysctl / cmdline parameter that makes it possible to have
hardlockup detector perform all-CPU backtrace.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The original watchdog_park_threads() function that was introduced by
commit 81a4beef91 ("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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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 9809b18fcf
Author: Michal Hocko <mhocko@suse.cz>
Date: Tue Sep 24 15:27:30 2013 -0700
watchdog: update watchdog_thresh properly
commit b3738d2932
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 9809b18fcf.
- Patch 4/4 utilizes watchdog_{suspend|resume} to replace some code that
was introduced by commit b3738d2932.
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: Ulrich Obergfell <uobergfe@redhat.com>
Reviewed-by: Aaron 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Guenter 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Reviewed-by: 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: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Chris Metcalf <cmetcalf@ezchip.com>
Acked-by: Don 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: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commit ab992dc38f ("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: Michal Hocko <mhocko@suse.cz>
Duh-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus 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 195daf665a ("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
b3738d2932 ("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: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Merge first patchbomb from Andrew Morton:
- arch/sh updates
- ocfs2 updates
- kernel/watchdog feature
- about half of mm/
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (122 commits)
Documentation: update arch list in the 'memtest' entry
Kconfig: memtest: update number of test patterns up to 17
arm: add support for memtest
arm64: add support for memtest
memtest: use phys_addr_t for physical addresses
mm: move memtest under mm
mm, hugetlb: abort __get_user_pages if current has been oom killed
mm, mempool: do not allow atomic resizing
memcg: print cgroup information when system panics due to panic_on_oom
mm: numa: remove migrate_ratelimited
mm: fold arch_randomize_brk into ARCH_HAS_ELF_RANDOMIZE
mm: split ET_DYN ASLR from mmap ASLR
s390: redefine randomize_et_dyn for ELF_ET_DYN_BASE
mm: expose arch_mmap_rnd when available
s390: standardize mmap_rnd() usage
powerpc: standardize mmap_rnd() usage
mips: extract logic for mmap_rnd()
arm64: standardize mmap_rnd() usage
x86: standardize mmap_rnd() usage
arm: factor out mmap ASLR into mmap_rnd
...
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: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Ulrich Obergfell
Don Zickus
Jiri Kosina
Yaowei Bai
Guenter Roeck
Frederic Weisbecker
Chris Metcalf
Michal Hocko
Peter Zijlstra
Linus Torvalds