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* watchdog/hardlockup: move SMP barriers from common code to buddy codeDouglas Anderson2023-06-191-0/+21
| | | | | | | | | | | | | | | | | It's been suggested that since the SMP barriers are only potentially useful for the buddy hardlockup detector, not the perf hardlockup detector, that the barriers belong in the buddy code. Let's move them and add clearer comments about why they're needed. Link: https://lkml.kernel.org/r/20230526184139.9.I5ab0a0eeb0bd52fb23f901d298c72fa5c396e22b@changeid Signed-off-by: Douglas Anderson <dianders@chromium.org> Suggested-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: "David S. Miller" <davem@davemloft.net> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
* watchdog/buddy: don't copy the cpumask in watchdog_next_cpu()Douglas Anderson2023-06-191-3/+2
| | | | | | | | | | | | | | | | There's no reason to make a copy of the "watchdog_cpus" locally in watchdog_next_cpu(). Making a copy wouldn't make things any more race free and we're just reading the value so there's no need for a copy. Link: https://lkml.kernel.org/r/20230526184139.7.If466f9a2b50884cbf6a1d8ad05525a2c17069407@changeid Signed-off-by: Douglas Anderson <dianders@chromium.org> Suggested-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: "David S. Miller" <davem@davemloft.net> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
* watchdog/buddy: cleanup how watchdog_buddy_check_hardlockup() is calledDouglas Anderson2023-06-191-1/+1
| | | | | | | | | | | | | | | | | | | | | | | In the patch ("watchdog/hardlockup: detect hard lockups using secondary (buddy) CPUs"), we added a call from the common watchdog.c file into the buddy. That call could be done more cleanly. Specifically: 1. If we move the call into watchdog_hardlockup_kick() then it keeps watchdog_timer_fn() simpler. 2. We don't need to pass an "unsigned long" to the buddy for the timer count. In the patch ("watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()") the count was changed to "atomic_t" which is backed by an int, so we should match types. Link: https://lkml.kernel.org/r/20230526184139.6.I006c7d958a1ea5c4e1e4dc44a25596d9bb5fd3ba@changeid Signed-off-by: Douglas Anderson <dianders@chromium.org> Suggested-by: Petr Mladek <pmladek@suse.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: "David S. Miller" <davem@davemloft.net> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
* watchdog/hardlockup: detect hard lockups using secondary (buddy) CPUsDouglas Anderson2023-06-091-0/+93
Implement a hardlockup detector that doesn't doesn't need any extra arch-specific support code to detect lockups. Instead of using something arch-specific we will use the buddy system, where each CPU watches out for another one. Specifically, each CPU will use its softlockup hrtimer to check that the next CPU is processing hrtimer interrupts by verifying that a counter is increasing. NOTE: unlike the other hard lockup detectors, the buddy one can't easily show what's happening on the CPU that locked up just by doing a simple backtrace. It relies on some other mechanism in the system to get information about the locked up CPUs. This could be support for NMI backtraces like [1], it could be a mechanism for printing the PC of locked CPUs at panic time like [2] / [3], or it could be something else. Even though that means we still rely on arch-specific code, this arch-specific code seems to often be implemented even on architectures that don't have a hardlockup detector. This style of hardlockup detector originated in some downstream Android trees and has been rebased on / carried in ChromeOS trees for quite a long time for use on arm and arm64 boards. Historically on these boards we've leveraged mechanism [2] / [3] to get information about hung CPUs, but we could move to [1]. Although the original motivation for the buddy system was for use on systems without an arch-specific hardlockup detector, it can still be useful to use even on systems that _do_ have an arch-specific hardlockup detector. On x86, for instance, there is a 24-part patch series [4] in progress switching the arch-specific hard lockup detector from a scarce perf counter to a less-scarce hardware resource. Potentially the buddy system could be a simpler alternative to free up the perf counter but still get hard lockup detection. Overall, pros (+) and cons (-) of the buddy system compared to an arch-specific hardlockup detector (which might be implemented using perf): + The buddy system is usable on systems that don't have an arch-specific hardlockup detector, like arm32 and arm64 (though it's being worked on for arm64 [5]). + The buddy system may free up scarce hardware resources. + If a CPU totally goes out to lunch (can't process NMIs) the buddy system could still detect the problem (though it would be unlikely to be able to get a stack trace). + The buddy system uses the same timer function to pet the hardlockup detector on the running CPU as it uses to detect hardlockups on other CPUs. Compared to other hardlockup detectors, this means it generates fewer interrupts and thus is likely better able to let CPUs stay idle longer. - If all CPUs are hard locked up at the same time the buddy system can't detect it. - If we don't have SMP we can't use the buddy system. - The buddy system needs an arch-specific mechanism (possibly NMI backtrace) to get info about the locked up CPU. [1] https://lore.kernel.org/r/20230419225604.21204-1-dianders@chromium.org [2] https://issuetracker.google.com/172213129 [3] https://docs.kernel.org/trace/coresight/coresight-cpu-debug.html [4] https://lore.kernel.org/lkml/20230301234753.28582-1-ricardo.neri-calderon@linux.intel.com/ [5] https://lore.kernel.org/linux-arm-kernel/20220903093415.15850-1-lecopzer.chen@mediatek.com/ Link: https://lkml.kernel.org/r/20230519101840.v5.14.I6bf789d21d0c3d75d382e7e51a804a7a51315f2c@changeid Signed-off-by: Colin Cross <ccross@android.com> Signed-off-by: Matthias Kaehlcke <mka@chromium.org> Signed-off-by: Guenter Roeck <groeck@chromium.org> Signed-off-by: Tzung-Bi Shih <tzungbi@chromium.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> Cc: Andi Kleen <ak@linux.intel.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Chen-Yu Tsai <wens@csie.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Daniel Thompson <daniel.thompson@linaro.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Ian Rogers <irogers@google.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Masayoshi Mizuma <msys.mizuma@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Petr Mladek <pmladek@suse.com> Cc: Pingfan Liu <kernelfans@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com> Cc: Ricardo Neri <ricardo.neri@intel.com> Cc: Stephane Eranian <eranian@google.com> Cc: Stephen Boyd <swboyd@chromium.org> Cc: Sumit Garg <sumit.garg@linaro.org> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>