From d6834d9c990333bfa433bc1816e2417f268eebbe Mon Sep 17 00:00:00 2001 From: Li Huafei Date: Tue, 22 Oct 2024 03:30:03 +0800 Subject: watchdog/hardlockup/perf: Fix perf_event memory leak During stress-testing, we found a kmemleak report for perf_event: unreferenced object 0xff110001410a33e0 (size 1328): comm "kworker/4:11", pid 288, jiffies 4294916004 hex dump (first 32 bytes): b8 be c2 3b 02 00 11 ff 22 01 00 00 00 00 ad de ...;...."....... f0 33 0a 41 01 00 11 ff f0 33 0a 41 01 00 11 ff .3.A.....3.A.... backtrace (crc 24eb7b3a): [<00000000e211b653>] kmem_cache_alloc_node_noprof+0x269/0x2e0 [<000000009d0985fa>] perf_event_alloc+0x5f/0xcf0 [<00000000084ad4a2>] perf_event_create_kernel_counter+0x38/0x1b0 [<00000000fde96401>] hardlockup_detector_event_create+0x50/0xe0 [<0000000051183158>] watchdog_hardlockup_enable+0x17/0x70 [<00000000ac89727f>] softlockup_start_fn+0x15/0x40 ... Our stress test includes CPU online and offline cycles, and updating the watchdog configuration. After reading the code, I found that there may be a race between cleaning up perf_event after updating watchdog and disabling event when the CPU goes offline: CPU0 CPU1 CPU2 (update watchdog) (hotplug offline CPU1) ... _cpu_down(CPU1) cpus_read_lock() // waiting for cpu lock softlockup_start_all smp_call_on_cpu(CPU1) softlockup_start_fn ... watchdog_hardlockup_enable(CPU1) perf create E1 watchdog_ev[CPU1] = E1 cpus_read_unlock() cpus_write_lock() cpuhp_kick_ap_work(CPU1) cpuhp_thread_fun ... watchdog_hardlockup_disable(CPU1) watchdog_ev[CPU1] = NULL dead_event[CPU1] = E1 __lockup_detector_cleanup for each dead_events_mask release each dead_event /* * CPU1 has not been added to * dead_events_mask, then E1 * will not be released */ CPU1 -> dead_events_mask cpumask_clear(&dead_events_mask) // dead_events_mask is cleared, E1 is leaked In this case, the leaked perf_event E1 matches the perf_event leak reported by kmemleak. Due to the low probability of problem recurrence (only reported once), I added some hack delays in the code: static void __lockup_detector_reconfigure(void) { ... watchdog_hardlockup_start(); cpus_read_unlock(); + mdelay(100); /* * Must be called outside the cpus locked section to prevent * recursive locking in the perf code. ... } void watchdog_hardlockup_disable(unsigned int cpu) { ... perf_event_disable(event); this_cpu_write(watchdog_ev, NULL); this_cpu_write(dead_event, event); + mdelay(100); cpumask_set_cpu(smp_processor_id(), &dead_events_mask); atomic_dec(&watchdog_cpus); ... } void hardlockup_detector_perf_cleanup(void) { ... perf_event_release_kernel(event); per_cpu(dead_event, cpu) = NULL; } + mdelay(100); cpumask_clear(&dead_events_mask); } Then, simultaneously performing CPU on/off and switching watchdog, it is almost certain to reproduce this leak. The problem here is that releasing perf_event is not within the CPU hotplug read-write lock. Commit: 941154bd6937 ("watchdog/hardlockup/perf: Prevent CPU hotplug deadlock") introduced deferred release to solve the deadlock caused by calling get_online_cpus() when releasing perf_event. Later, commit: efe951d3de91 ("perf/x86: Fix perf,x86,cpuhp deadlock") removed the get_online_cpus() call on the perf_event release path to solve another deadlock problem. Therefore, it is now possible to move the release of perf_event back into the CPU hotplug read-write lock, and release the event immediately after disabling it. Fixes: 941154bd6937 ("watchdog/hardlockup/perf: Prevent CPU hotplug deadlock") Signed-off-by: Li Huafei Signed-off-by: Ingo Molnar Cc: Thomas Gleixner Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20241021193004.308303-1-lihuafei1@huawei.com --- kernel/watchdog.c | 25 ------------------------- 1 file changed, 25 deletions(-) (limited to 'kernel/watchdog.c') diff --git a/kernel/watchdog.c b/kernel/watchdog.c index b2da7de39d06..18156023e461 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -347,8 +347,6 @@ static int __init watchdog_thresh_setup(char *str) } __setup("watchdog_thresh=", watchdog_thresh_setup); -static void __lockup_detector_cleanup(void); - #ifdef CONFIG_SOFTLOCKUP_DETECTOR_INTR_STORM enum stats_per_group { STATS_SYSTEM, @@ -886,11 +884,6 @@ static void __lockup_detector_reconfigure(void) watchdog_hardlockup_start(); cpus_read_unlock(); - /* - * Must be called outside the cpus locked section to prevent - * recursive locking in the perf code. - */ - __lockup_detector_cleanup(); } void lockup_detector_reconfigure(void) @@ -940,24 +933,6 @@ static inline void lockup_detector_setup(void) } #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */ -static void __lockup_detector_cleanup(void) -{ - lockdep_assert_held(&watchdog_mutex); - hardlockup_detector_perf_cleanup(); -} - -/** - * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes - * - * Caller must not hold the cpu hotplug rwsem. - */ -void lockup_detector_cleanup(void) -{ - mutex_lock(&watchdog_mutex); - __lockup_detector_cleanup(); - mutex_unlock(&watchdog_mutex); -} - /** * lockup_detector_soft_poweroff - Interface to stop lockup detector(s) * -- cgit v1.2.3