[PATCH v4 -next 1/2] watchdog/hardlockup/perf: Fix perf_event memory leak
From: Li Huafei
Date: Fri Sep 13 2024 - 05:39:32 EST
During the stress test, 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, 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. The 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, the 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@xxxxxxxxxx>
---
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 a8dfb38c9bb6..e78fa535f61d 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 b1fd2a3db91a..19d9ddb61e0d 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 830a83895493..1935b40813bc 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 59c1d86a73a2..2fdb96eaf493 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
*
--
2.25.1