From: Ran Xiaokai <[email protected]>
Lockdep reports this deadlock log:
osnoise: could not start sampling thread
============================================
WARNING: possible recursive locking detected
--------------------------------------------
CPU0
----
lock(cpu_hotplug_lock);
lock(cpu_hotplug_lock);
Call Trace:
<TASK>
print_deadlock_bug+0x282/0x3c0
__lock_acquire+0x1610/0x29a0
lock_acquire+0xcb/0x2d0
cpus_read_lock+0x49/0x120
stop_per_cpu_kthreads+0x7/0x60
start_kthread+0x103/0x120
osnoise_hotplug_workfn+0x5e/0x90
process_one_work+0x44f/0xb30
worker_thread+0x33e/0x5e0
kthread+0x206/0x3b0
ret_from_fork+0x31/0x50
ret_from_fork_asm+0x11/0x20
</TASK>
This is the deadlock scenario:
osnoise_hotplug_workfn()
guard(cpus_read_lock)(); // first lock call
start_kthread(cpu)
if (IS_ERR(kthread)) {
stop_per_cpu_kthreads(); {
cpus_read_lock(); // second lock call. Cause the AA deadlock
}
}
It is not necessary to call stop_per_cpu_kthreads() which stops osnoise
kthread for every other CPUs in the system if a failure occurs during
hotplug of a certain CPU.
For start_per_cpu_kthreads(), if the start_kthread() call fails,
this function calls stop_per_cpu_kthreads() to handle the error.
Therefore, similarly, there is no need to call stop_per_cpu_kthreads()
again within start_kthread().
So just remove stop_per_cpu_kthreads() from start_kthread to solve this issue.
Fixes: c8895e271f79 ("trace/osnoise: Support hotplug operations")
Signed-off-by: Ran Xiaokai <[email protected]>
---
kernel/trace/trace_osnoise.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 647516a73fa2..e732c9e37e14 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -2006,7 +2006,6 @@ static int start_kthread(unsigned int cpu)
if (IS_ERR(kthread)) {
pr_err(BANNER "could not start sampling thread\n");
- stop_per_cpu_kthreads();
return -ENOMEM;
}
--
2.17.1
