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28168eca32
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>
114 lines
3.0 KiB
C
114 lines
3.0 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/cpu.h>
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#include <linux/cpumask.h>
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#include <linux/kernel.h>
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#include <linux/nmi.h>
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#include <linux/percpu-defs.h>
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static cpumask_t __read_mostly watchdog_cpus;
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static unsigned int watchdog_next_cpu(unsigned int cpu)
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{
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unsigned int next_cpu;
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next_cpu = cpumask_next(cpu, &watchdog_cpus);
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if (next_cpu >= nr_cpu_ids)
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next_cpu = cpumask_first(&watchdog_cpus);
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if (next_cpu == cpu)
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return nr_cpu_ids;
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return next_cpu;
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}
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int __init watchdog_hardlockup_probe(void)
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{
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return 0;
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}
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void watchdog_hardlockup_enable(unsigned int cpu)
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{
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unsigned int next_cpu;
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/*
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* The new CPU will be marked online before the hrtimer interrupt
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* gets a chance to run on it. If another CPU tests for a
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* hardlockup on the new CPU before it has run its the hrtimer
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* interrupt, it will get a false positive. Touch the watchdog on
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* the new CPU to delay the check for at least 3 sampling periods
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* to guarantee one hrtimer has run on the new CPU.
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*/
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watchdog_hardlockup_touch_cpu(cpu);
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/*
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* We are going to check the next CPU. Our watchdog_hrtimer
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* need not be zero if the CPU has already been online earlier.
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* Touch the watchdog on the next CPU to avoid false positive
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* if we try to check it in less then 3 interrupts.
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*/
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next_cpu = watchdog_next_cpu(cpu);
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if (next_cpu < nr_cpu_ids)
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watchdog_hardlockup_touch_cpu(next_cpu);
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/*
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* Makes sure that watchdog is touched on this CPU before
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* other CPUs could see it in watchdog_cpus. The counter
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* part is in watchdog_buddy_check_hardlockup().
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*/
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smp_wmb();
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cpumask_set_cpu(cpu, &watchdog_cpus);
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}
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void watchdog_hardlockup_disable(unsigned int cpu)
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{
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unsigned int next_cpu = watchdog_next_cpu(cpu);
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/*
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* Offlining this CPU will cause the CPU before this one to start
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* checking the one after this one. If this CPU just finished checking
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* the next CPU and updating hrtimer_interrupts_saved, and then the
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* previous CPU checks it within one sample period, it will trigger a
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* false positive. Touch the watchdog on the next CPU to prevent it.
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*/
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if (next_cpu < nr_cpu_ids)
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watchdog_hardlockup_touch_cpu(next_cpu);
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/*
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* Makes sure that watchdog is touched on the next CPU before
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* this CPU disappear in watchdog_cpus. The counter part is in
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* watchdog_buddy_check_hardlockup().
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*/
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smp_wmb();
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cpumask_clear_cpu(cpu, &watchdog_cpus);
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}
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void watchdog_buddy_check_hardlockup(int hrtimer_interrupts)
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{
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unsigned int next_cpu;
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/*
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* Test for hardlockups every 3 samples. The sample period is
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* watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
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* watchdog_thresh (over by 20%).
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*/
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if (hrtimer_interrupts % 3 != 0)
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return;
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/* check for a hardlockup on the next CPU */
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next_cpu = watchdog_next_cpu(smp_processor_id());
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if (next_cpu >= nr_cpu_ids)
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return;
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/*
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* Make sure that the watchdog was touched on next CPU when
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* watchdog_next_cpu() returned another one because of
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* a change in watchdog_hardlockup_enable()/disable().
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*/
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smp_rmb();
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watchdog_hardlockup_check(next_cpu, NULL);
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}
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