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Refactor hardlockup_detector_event_create() to be stateless. Return the created perf_event pointer to the caller instead of directly modifying the per-cpu 'watchdog_ev' variable. This allows the probe path to safely manage a temporary event without the risk of leaving stale pointers should task migration occur. Use cpu_hotplug_disable() during the probe to ensure the target CPU remains stable throughout the availability check. Signed-off-by: Shouxin Sun Signed-off-by: Junnan Zhang Signed-off-by: Qiliang Yuan Cc: Song Liu Cc: Douglas Anderson Cc: Jinchao Wang --- v6: - Change title to "simplify/cleanup" and remove "Fixes" tag since the issue is not reproducible on mainline. - Rewrite commit message in imperative mood. - Clarify that mainline is safe while this improves robustness. - v5 link: https://lore.kernel.org/all/20260127022238.1182079-1-realwujing@gmail.com/ v5: - Refine description: clarify that the retry path uses worker threads without PF_PERCPU_THREAD (though mainline is safe due to system_percpu_wq). - v4 link: https://lore.kernel.org/all/20260124070814.806828-1-realwujing@gmail.com/ v4: - Add cpu_hotplug_disable() in watchdog_hardlockup_probe() to stabilize the probe CPU. - Update description to explain the relevance of 4.19 logs. v3: - Refactor hardlockup_detector_event_create() to be stateless by returning the event pointer instead of directly assigning to per-cpu variables. - Restore PMU cycle fallback and unify the enable/probe paths. v2: - Add Cc: stable@vger.kernel.org. v1: - Avoid 'watchdog_ev' in probe path by manually creating and releasing a local perf event. kernel/watchdog_perf.c | 56 +++++++++++++++++++++++++----------------- 1 file changed, 34 insertions(+), 22 deletions(-) diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c index d3ca70e3c256..887b61c65c1b 100644 --- a/kernel/watchdog_perf.c +++ b/kernel/watchdog_perf.c @@ -17,6 +17,7 @@ #include #include #include +#include #include #include @@ -118,18 +119,11 @@ static void watchdog_overflow_callback(struct perf_event *event, watchdog_hardlockup_check(smp_processor_id(), regs); } -static int hardlockup_detector_event_create(void) +static struct perf_event *hardlockup_detector_event_create(unsigned int cpu) { - unsigned int cpu; struct perf_event_attr *wd_attr; struct perf_event *evt; - /* - * Preemption is not disabled because memory will be allocated. - * Ensure CPU-locality by calling this in per-CPU kthread. - */ - WARN_ON(!is_percpu_thread()); - cpu = raw_smp_processor_id(); wd_attr = &wd_hw_attr; wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); @@ -143,14 +137,7 @@ static int hardlockup_detector_event_create(void) watchdog_overflow_callback, NULL); } - if (IS_ERR(evt)) { - pr_debug("Perf event create on CPU %d failed with %ld\n", cpu, - PTR_ERR(evt)); - return PTR_ERR(evt); - } - WARN_ONCE(this_cpu_read(watchdog_ev), "unexpected watchdog_ev leak"); - this_cpu_write(watchdog_ev, evt); - return 0; + return evt; } /** @@ -159,17 +146,26 @@ static int hardlockup_detector_event_create(void) */ void watchdog_hardlockup_enable(unsigned int cpu) { + struct perf_event *evt; + WARN_ON_ONCE(cpu != smp_processor_id()); - if (hardlockup_detector_event_create()) + evt = hardlockup_detector_event_create(cpu); + if (IS_ERR(evt)) { + pr_debug("Perf event create on CPU %d failed with %ld\n", cpu, + PTR_ERR(evt)); return; + } /* use original value for check */ if (!atomic_fetch_inc(&watchdog_cpus)) pr_info("Enabled. Permanently consumes one hw-PMU counter.\n"); + WARN_ONCE(this_cpu_read(watchdog_ev), "unexpected watchdog_ev leak"); + this_cpu_write(watchdog_ev, evt); + watchdog_init_timestamp(); - perf_event_enable(this_cpu_read(watchdog_ev)); + perf_event_enable(evt); } /** @@ -263,19 +259,35 @@ bool __weak __init arch_perf_nmi_is_available(void) */ int __init watchdog_hardlockup_probe(void) { + struct perf_event *evt; + unsigned int cpu; int ret; if (!arch_perf_nmi_is_available()) return -ENODEV; - ret = hardlockup_detector_event_create(); + if (!hw_nmi_get_sample_period(watchdog_thresh)) + return -EINVAL; - if (ret) { + /* + * Test hardware PMU availability by creating a temporary perf event. + * The requested CPU is arbitrary; preemption is not disabled, so + * raw_smp_processor_id() is used. Surround with cpu_hotplug_disable() + * to ensure the arbitrarily chosen CPU remains online during the check. + * The event is released immediately. + */ + cpu_hotplug_disable(); + cpu = raw_smp_processor_id(); + evt = hardlockup_detector_event_create(cpu); + if (IS_ERR(evt)) { pr_info("Perf NMI watchdog permanently disabled\n"); + ret = PTR_ERR(evt); } else { - perf_event_release_kernel(this_cpu_read(watchdog_ev)); - this_cpu_write(watchdog_ev, NULL); + perf_event_release_kernel(evt); + ret = 0; } + cpu_hotplug_enable(); + return ret; } -- 2.51.0