6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Li Huafei lihuafei1@huawei.com
[ Upstream commit d6834d9c990333bfa433bc1816e2417f268eebbe ]
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 lihuafei1@huawei.com Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra peterz@infradead.org Link: https://lore.kernel.org/r/20241021193004.308303-1-lihuafei1@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/nmi.h | 4 ---- kernel/cpu.c | 5 ----- kernel/watchdog.c | 25 ------------------------- kernel/watchdog_perf.c | 28 +--------------------------- 4 files changed, 1 insertion(+), 61 deletions(-)
diff --git a/include/linux/nmi.h b/include/linux/nmi.h index a8dfb38c9bb6f..e78fa535f61dd 100644 --- a/include/linux/nmi.h +++ b/include/linux/nmi.h @@ -17,7 +17,6 @@ void lockup_detector_init(void); void lockup_detector_retry_init(void); void lockup_detector_soft_poweroff(void); -void lockup_detector_cleanup(void);
extern int watchdog_user_enabled; extern int watchdog_thresh; @@ -37,7 +36,6 @@ extern int sysctl_hardlockup_all_cpu_backtrace; static inline void lockup_detector_init(void) { } static inline void lockup_detector_retry_init(void) { } static inline void lockup_detector_soft_poweroff(void) { } -static inline void lockup_detector_cleanup(void) { } #endif /* !CONFIG_LOCKUP_DETECTOR */
#ifdef CONFIG_SOFTLOCKUP_DETECTOR @@ -104,12 +102,10 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs); #if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF) extern void hardlockup_detector_perf_stop(void); extern void hardlockup_detector_perf_restart(void); -extern void hardlockup_detector_perf_cleanup(void); extern void hardlockup_config_perf_event(const char *str); #else static inline void hardlockup_detector_perf_stop(void) { } static inline void hardlockup_detector_perf_restart(void) { } -static inline void hardlockup_detector_perf_cleanup(void) { } static inline void hardlockup_config_perf_event(const char *str) { } #endif
diff --git a/kernel/cpu.c b/kernel/cpu.c index 9ee6c9145b1df..cf02a629f9902 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1452,11 +1452,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
out: cpus_write_unlock(); - /* - * Do post unplug cleanup. This is still protected against - * concurrent CPU hotplug via cpu_add_remove_lock. - */ - lockup_detector_cleanup(); arch_smt_update(); return ret; } diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 262691ba62b7a..4dc72540c3b0f 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, @@ -878,11 +876,6 @@ 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) @@ -932,24 +925,6 @@ 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) * diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c index 59c1d86a73a24..2fdb96eaf4933 100644 --- a/kernel/watchdog_perf.c +++ b/kernel/watchdog_perf.c @@ -21,8 +21,6 @@ #include <linux/perf_event.h>
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev); -static DEFINE_PER_CPU(struct perf_event *, dead_event); -static struct cpumask dead_events_mask;
static atomic_t watchdog_cpus = ATOMIC_INIT(0);
@@ -181,36 +179,12 @@ void watchdog_hardlockup_disable(unsigned int cpu)
if (event) { perf_event_disable(event); + perf_event_release_kernel(event); this_cpu_write(watchdog_ev, NULL); - this_cpu_write(dead_event, event); - cpumask_set_cpu(smp_processor_id(), &dead_events_mask); atomic_dec(&watchdog_cpus); } }
-/** - * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them - * - * Called from lockup_detector_cleanup(). Serialized by the caller. - */ -void hardlockup_detector_perf_cleanup(void) -{ - int cpu; - - for_each_cpu(cpu, &dead_events_mask) { - struct perf_event *event = per_cpu(dead_event, cpu); - - /* - * Required because for_each_cpu() reports unconditionally - * CPU0 as set on UP kernels. Sigh. - */ - if (event) - perf_event_release_kernel(event); - per_cpu(dead_event, cpu) = NULL; - } - cpumask_clear(&dead_events_mask); -} - /** * hardlockup_detector_perf_stop - Globally stop watchdog events *