From: Ran Xiaokai ran.xiaokai@zte.com.cn

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 ran.xiaokai@zte.com.cn --- 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; }