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)
...
...
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. What's more, it seems that smp_call_on_cpu doesn't need protection from
cpu_hotplug_lock. I try to revert the old patch to fix this problem, but I
encountered some conflicts. Or I should just release and acquire
cpu_hotplug_lock
during between smp_call_on_cpu? I'm looking forward any suggestion :).
Fixes: e31d6883f21c ("watchdog/core, powerpc: Lock cpus across reconfiguration")
Signed-off-by: Luo Gengkun <luogeng...@huaweicloud.com>
---
arch/powerpc/kernel/watchdog.c | 4 ++++
kernel/watchdog.c | 9 ---------
2 files changed, 4 insertions(+), 9 deletions(-)
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index 8c464a5d8246..f33f532ea7fa 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -550,17 +550,21 @@ void watchdog_hardlockup_stop(void)
{
int cpu;
+ cpus_read_lock();
for_each_cpu(cpu, &wd_cpus_enabled)
stop_watchdog_on_cpu(cpu);
+ cpus_read_unlock();
}
void watchdog_hardlockup_start(void)
{
int cpu;
+ cpus_read_lock();
watchdog_calc_timeouts();
for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
start_watchdog_on_cpu(cpu);
+ cpus_read_unlock();
}
/*
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51915b44ac73..13303a932cde 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -867,7 +867,6 @@ int lockup_detector_offline_cpu(unsigned int cpu)
static void __lockup_detector_reconfigure(void)
{
- cpus_read_lock();
watchdog_hardlockup_stop();
softlockup_stop_all();
@@ -877,12 +876,6 @@ static void __lockup_detector_reconfigure(void)
softlockup_start_all();
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)
@@ -916,11 +909,9 @@ static __init void lockup_detector_setup(void)
#else /* CONFIG_SOFTLOCKUP_DETECTOR */
static void __lockup_detector_reconfigure(void)
{
- cpus_read_lock();
watchdog_hardlockup_stop();
lockup_detector_update_enable();
watchdog_hardlockup_start();
- cpus_read_unlock();
}
void lockup_detector_reconfigure(void)
{
--
2.34.1
