The patch titled
Subject: watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Douglas Anderson <dianders@xxxxxxxxxxxx>
Subject: watchdog/hardlockup: add a "cpu" param to watchdog_hardlockup_check()
Date: Fri, 19 May 2023 10:18:34 -0700
In preparation for the buddy hardlockup detector where the CPU checking
for lockup might not be the currently running CPU, add a "cpu" parameter
to watchdog_hardlockup_check().
As part of this change, make hrtimer_interrupts an atomic_t since now the
CPU incrementing the value and the CPU reading the value might be
different. Technially this could also be done with just READ_ONCE and
WRITE_ONCE, but atomic_t feels a little cleaner in this case.
While hrtimer_interrupts is made atomic_t, we change
hrtimer_interrupts_saved from "unsigned long" to "int". The "int" is
needed to match the data type backing atomic_t for hrtimer_interrupts.
Even if this changes us from 64-bits to 32-bits (which I don't think is
true for most compilers), it doesn't really matter. All we ever do is
increment it every few seconds and compare it to an old value so 32-bits
is fine (even 16-bits would be). The "signed" vs "unsigned" also doesn't
matter for simple equality comparisons.
hrtimer_interrupts_saved is _not_ switched to atomic_t nor even accessed
with READ_ONCE / WRITE_ONCE. The hrtimer_interrupts_saved is always
consistently accessed with the same CPU. NOTE: with the upcoming "buddy"
detector there is one special case. When a CPU goes offline/online then
we can change which CPU is the one to consistently access a given instance
of hrtimer_interrupts_saved. We still can't end up with a partially
updated hrtimer_interrupts_saved, however, because we end up petting all
affected CPUs to make sure the new and old CPU can't end up somehow
read/write hrtimer_interrupts_saved at the same time.
Link: https://lkml.kernel.org/r/20230519101840.v5.10.I3a7d4dd8c23ac30ee0b607d77feb6646b64825c0@changeid
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Chen-Yu Tsai <wens@xxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxxx>
Cc: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Guenter Roeck <groeck@xxxxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>
Cc: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>
Cc: Ricardo Neri <ricardo.neri@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Cc: Sumit Garg <sumit.garg@xxxxxxxxxx>
Cc: Tzung-Bi Shih <tzungbi@xxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/nmi.h | 2 -
kernel/watchdog.c | 52 ++++++++++++++++++++++++---------------
kernel/watchdog_perf.c | 2 -
3 files changed, 34 insertions(+), 22 deletions(-)
--- a/include/linux/nmi.h~watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check
+++ a/include/linux/nmi.h
@@ -88,7 +88,7 @@ static inline void hardlockup_detector_d
#endif
#if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF)
-void watchdog_hardlockup_check(struct pt_regs *regs);
+void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs);
#endif
#if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
--- a/kernel/watchdog.c~watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check
+++ a/kernel/watchdog.c
@@ -87,29 +87,34 @@ __setup("nmi_watchdog=", hardlockup_pani
#if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF)
-static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
-static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
+static DEFINE_PER_CPU(atomic_t, hrtimer_interrupts);
+static DEFINE_PER_CPU(int, hrtimer_interrupts_saved);
static DEFINE_PER_CPU(bool, watchdog_hardlockup_warned);
static unsigned long watchdog_hardlockup_all_cpu_dumped;
-static bool is_hardlockup(void)
+static bool is_hardlockup(unsigned int cpu)
{
- unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
+ int hrint = atomic_read(&per_cpu(hrtimer_interrupts, cpu));
- if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
+ if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
return true;
- __this_cpu_write(hrtimer_interrupts_saved, hrint);
+ /*
+ * NOTE: we don't need any fancy atomic_t or READ_ONCE/WRITE_ONCE
+ * for hrtimer_interrupts_saved. hrtimer_interrupts_saved is
+ * written/read by a single CPU.
+ */
+ per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
return false;
}
static void watchdog_hardlockup_kick(void)
{
- __this_cpu_inc(hrtimer_interrupts);
+ atomic_inc(raw_cpu_ptr(&hrtimer_interrupts));
}
-void watchdog_hardlockup_check(struct pt_regs *regs)
+void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
{
/*
* Check for a hardlockup by making sure the CPU's timer
@@ -117,35 +122,42 @@ void watchdog_hardlockup_check(struct pt
* fired multiple times before we overflow'd. If it hasn't
* then this is a good indication the cpu is stuck
*/
- if (is_hardlockup()) {
+ if (is_hardlockup(cpu)) {
unsigned int this_cpu = smp_processor_id();
+ struct cpumask backtrace_mask = *cpu_online_mask;
/* Only print hardlockups once. */
- if (__this_cpu_read(watchdog_hardlockup_warned))
+ if (per_cpu(watchdog_hardlockup_warned, cpu))
return;
- pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n", this_cpu);
+ pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n", cpu);
print_modules();
print_irqtrace_events(current);
- if (regs)
- show_regs(regs);
- else
- dump_stack();
+ if (cpu == this_cpu) {
+ if (regs)
+ show_regs(regs);
+ else
+ dump_stack();
+ cpumask_clear_cpu(cpu, &backtrace_mask);
+ } else {
+ if (trigger_single_cpu_backtrace(cpu))
+ cpumask_clear_cpu(cpu, &backtrace_mask);
+ }
/*
- * Perform all-CPU dump only once to avoid multiple hardlockups
- * generating interleaving traces
+ * Perform multi-CPU dump only once to avoid multiple
+ * hardlockups generating interleaving traces
*/
if (sysctl_hardlockup_all_cpu_backtrace &&
!test_and_set_bit(0, &watchdog_hardlockup_all_cpu_dumped))
- trigger_allbutself_cpu_backtrace();
+ trigger_cpumask_backtrace(&backtrace_mask);
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
- __this_cpu_write(watchdog_hardlockup_warned, true);
+ per_cpu(watchdog_hardlockup_warned, cpu) = true;
} else {
- __this_cpu_write(watchdog_hardlockup_warned, false);
+ per_cpu(watchdog_hardlockup_warned, cpu) = false;
}
}
--- a/kernel/watchdog_perf.c~watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check
+++ a/kernel/watchdog_perf.c
@@ -120,7 +120,7 @@ static void watchdog_overflow_callback(s
return;
}
- watchdog_hardlockup_check(regs);
+ watchdog_hardlockup_check(smp_processor_id(), regs);
}
static int hardlockup_detector_event_create(void)
_
Patches currently in -mm which might be from dianders@xxxxxxxxxxxx are
migrate_pages-avoid-blocking-for-io-in-migrate_sync_light.patch
watchdog-perf-define-dummy-watchdog_update_hrtimer_threshold-on-correct-config.patch
watchdog-perf-more-properly-prevent-false-positives-with-turbo-modes.patch
watchdog-hardlockup-add-comments-to-touch_nmi_watchdog.patch
watchdog-perf-rename-watchdog_hldc-to-watchdog_perfc.patch
watchdog-hardlockup-move-perf-hardlockup-checking-panic-to-common-watchdogc.patch
watchdog-hardlockup-style-changes-to-watchdog_hardlockup_check-is_hardlockup.patch
watchdog-hardlockup-add-a-cpu-param-to-watchdog_hardlockup_check.patch
watchdog-hardlockup-move-perf-hardlockup-watchdog-petting-to-watchdogc.patch
watchdog-hardlockup-rename-some-nmi-watchdog-constants-function.patch
watchdog-hardlockup-have-the-perf-hardlockup-use-__weak-functions-more-cleanly.patch
watchdog-hardlockup-detect-hard-lockups-using-secondary-buddy-cpus.patch
watchdog-perf-add-a-weak-function-for-an-arch-to-detect-if-perf-can-use-nmis.patch
arm64-enable-perf-events-based-hard-lockup-detector.patch
