15 Nov, 2020
1 commit
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Define watchdog_allowed_mask only when SOFTLOCKUP_DETECTOR is enabled.
Fixes: 7feeb9cd4f5b ("watchdog/sysctl: Clean up sysctl variable name space")
Signed-off-by: Santosh Sivaraj
Signed-off-by: Andrew Morton
Reviewed-by: Petr Mladek
Cc: Thomas Gleixner
Link: https://lkml.kernel.org/r/20201106015025.1281561-1-santosh@fossix.org
Signed-off-by: Linus Torvalds
09 Jun, 2020
1 commit
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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
Signed-off-by: Andrew Morton
Acked-by: Vlastimil Babka
Cc: Kees Cook
Cc: Iurii Zaikin
Cc: Luis Chamberlain
Link: http://lkml.kernel.org/r/20200507214624.21911-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds
27 Apr, 2020
1 commit
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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
Acked-by: Andrey Ignatov
Signed-off-by: Al Viro
17 Jan, 2020
1 commit
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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
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/87o8v3uuzl.fsf@nanos.tec.linutronix.de
16 Jan, 2020
2 commits
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commit 9cf57731b63e ("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 b1a8de1f5343
("softlockup: make detector be aware of task switch of processes hogging
cpu")Signed-off-by: Petr Mladek
Signed-off-by: Thomas Gleixner
Acked-by: Peter Ziljstra
Link: https://lore.kernel.org/r/20191024114928.15377-2-pmladek@suse.com -
After commit 9cf57731b63e ("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
Signed-off-by: Thomas Gleixner
Link: https://lore.kernel.org/r/20191218131720.4146aea2@xhacker.debian
02 Aug, 2019
1 commit
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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
Signed-off-by: Thomas Gleixner
Acked-by: Peter Zijlstra (Intel)
Link: https://lkml.kernel.org/r/20190726185753.262895510@linutronix.de
18 Apr, 2019
1 commit
-
Signed-off-by: Arash Fotouhi
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
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
28 Mar, 2019
1 commit
-
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: 9cf57731b63e ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Reported-by: Maxime Coquelin
Signed-off-by: Thomas Gleixner
Tested-by: Maxime Coquelin
Cc: Peter Zijlstra
Cc: Oleg Nesterov
Cc: Michael Ellerman
Cc: Nicholas Piggin
Cc: Don Zickus
Cc: Ricardo Neri
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1903262245490.1789@nanos.tec.linutronix.de
22 Mar, 2019
1 commit
-
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
Signed-off-by: Thomas Gleixner
Link: https://lkml.kernel.org/r/7855.1552383228@turing-police
01 Nov, 2018
1 commit
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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
Signed-off-by: Thomas Gleixner
Cc: rdunlap@infradead.org
Cc: prarit@redhat.com
Link: https://lkml.kernel.org/r/1541079018-13953-1-git-send-email-loberman@redhat.com
30 Aug, 2018
1 commit
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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 ce4f06dcbb5d ("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: ce4f06dcbb5d ("stop_machine: Touch_nmi_watchdog() after MULTI_STOP_PREPARE")
Signed-off-by: Vincent Whitchurch
Signed-off-by: Thomas Gleixner
Cc: Peter Zijlstra
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
16 Jul, 2018
1 commit
-
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
Tested-by: Rong Chen
Signed-off-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Fixes: 9cf57731b63e ("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
03 Jul, 2018
1 commit
-
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
Signed-off-by: Peter Zijlstra (Intel)
Cc: Linus Torvalds
Cc: Peter Zijlstra
Cc: Thomas Gleixner
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar
08 Nov, 2017
1 commit
-
Signed-off-by: Ingo Molnar
02 Nov, 2017
1 commit
-
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
Reviewed-by: Philippe Ombredanne
Reviewed-by: Thomas Gleixner
Signed-off-by: Greg Kroah-Hartman
27 Oct, 2017
3 commits
-
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
Acked-by: Thomas Gleixner
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Linus Torvalds
Cc: Luiz Capitulino
Cc: Mike Galbraith
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Rik van Riel
Cc: Wanpeng Li
Link: http://lkml.kernel.org/r/1509072159-31808-9-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar -
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
Acked-by: Thomas Gleixner
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Linus Torvalds
Cc: Luiz Capitulino
Cc: Mike Galbraith
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Rik van Riel
Cc: Wanpeng Li
Link: http://lkml.kernel.org/r/1509072159-31808-3-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar -
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
Acked-by: Thomas Gleixner
Acked-by: Paul E. McKenney
Cc: Chris Metcalf
Cc: Christoph Lameter
Cc: Linus Torvalds
Cc: Luiz Capitulino
Cc: Mike Galbraith
Cc: Peter Zijlstra
Cc: Rik van Riel
Cc: Wanpeng Li
Link: http://lkml.kernel.org/r/1509072159-31808-2-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar
04 Oct, 2017
5 commits
-
The variable is unused when the softlockup detector is disabled in Kconfig.
Signed-off-by: Thomas Gleixner
-
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
Cc: Linus Torvalds
Cc: Michael Ellerman
Cc: Peter Zijlstra
Cc: Don Zickus -
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/0xbcAnd 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/0xbcThis 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
Signed-off-by: Thomas Gleixner
Acked-by: Michael Ellerman
Cc: Benjamin Herrenschmidt
Cc: Nicholas Piggin
Cc: linuxppc-dev@lists.ozlabs.org -
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
Signed-off-by: Thomas Gleixner
Acked-by: Michael Ellerman
Cc: Peter Zijlstra
Cc: Don Zickus
Cc: Benjamin Herrenschmidt
Cc: Nicholas Piggin
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710022105570.2114@nanos -
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: 6592ad2fcc8f ("watchdog/core, powerpc: Make watchdog_nmi_reconfigure() two stage")
Requested-by: Linus 'Nursing his pet-peeve' Torvalds
Signed-off-by: Thomas 'Mopping up garbage' Gleixner
Acked-by: Michael Ellerman
Cc: Peter Zijlstra
Cc: Don Zickus
Cc: Benjamin Herrenschmidt
Cc: Nicholas Piggin
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710021957480.2114@nanos
14 Sep, 2017
16 commits
-
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Benjamin Herrenschmidt
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Michael Ellerman
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20170912194148.418497420@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194148.259651788@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194148.099799541@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.939985640@linutronix.de
Signed-off-by: Ingo Molnar -
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 NMIsRight 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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Benjamin Herrenschmidt
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Michael Ellerman
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20170912194147.862865570@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.783210221@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.549114957@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.470370113@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.377182587@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.297288838@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.218075991@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.139629546@linutronix.de
Signed-off-by: Ingo Molnar -
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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194147.045545271@linutronix.de
Signed-off-by: Ingo Molnar -
Commit:
b94f51183b06 ("kernel/watchdog: prevent false hardlockup on overloaded system")
tries to fix the following issue:
proc_write()
set_sample_period() park()
disable_nmi()
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1709052038270.2393@nanos
Signed-off-by: Ingo Molnar -
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
Reported-by: Borislav Petkov
Signed-off-by: Thomas Gleixner
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194146.884469246@linutronix.de
Signed-off-by: Ingo Molnar -
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() 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
Reviewed-by: Don Zickus
Cc: Andrew Morton
Cc: Borislav Petkov
Cc: Chris Metcalf
Cc: Linus Torvalds
Cc: Nicholas Piggin
Cc: Peter Zijlstra
Cc: Sebastian Siewior
Cc: Ulrich Obergfell
Link: http://lkml.kernel.org/r/20170912194146.806708429@linutronix.de
Signed-off-by: Ingo Molnar