We found an AA deadlock problem as shown belowed:
TaskA TaskB WatchDog
system_wq
...
css_killed_work_fn:
P(cgroup_mutex)
...
...
__lockup_detector_reconfigure:
P(cpu_hotplug_lock.read)
...
...
cpu_up:
percpu_down_write:
P(cpu_hotplug_lock.write)
...
cgroup_bpf_release:
P(cgroup_mutex)
smp_call_on_cpu:
Wait system_wq
cpuset_css_offline:
P(cpu_hotplug_lock.read)
WatchDog is waitting for system_wq, who is waitting for cgroup_mutex, to finish
the jobs, but the owner of the cgroup_mutex is waitting for cpu_hotplug_lock.
The key point is the cpu_hotplug_lock, cause the system_wq may be waitting other
lock. It seems unhealthy to hold a lock when waitting system_wq, because we
never know what jobs are system_wq doing. So I fix this by replace
cpu_read_lock/unlock
with cpu_hotplug_disable/enable to prevent cpu offline/online.
Fixes: e31d6883f21c ("watchdog/core, powerpc: Lock cpus across reconfiguration")
Signed-off-by: Luo Gengkun <[email protected]>
---
kernel/watchdog.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51915b44ac73..6ac6fb8d3be0 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -867,7 +867,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
static void __lockup_detector_reconfigure(void)
{
- cpus_read_lock();
+ cpu_hotplug_disable();
watchdog_hardlockup_stop();
softlockup_stop_all();
@@ -877,7 +877,7 @@ static void __lockup_detector_reconfigure(void)
softlockup_start_all();
watchdog_hardlockup_start();
- cpus_read_unlock();
+ cpu_hotplug_enable();
/*
* Must be called outside the cpus locked section to prevent
* recursive locking in the perf code.
@@ -916,11 +916,11 @@ static __init void lockup_detector_setup(void)
#else /* CONFIG_SOFTLOCKUP_DETECTOR */
static void __lockup_detector_reconfigure(void)
{
- cpus_read_lock();
+ cpu_hotplug_disable();
watchdog_hardlockup_stop();
lockup_detector_update_enable();
watchdog_hardlockup_start();
- cpus_read_unlock();
+ cpu_hotplug_enable();
}
void lockup_detector_reconfigure(void)
{
--
2.34.1
