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tracing/osnoise: Fix possible recursive locking in stop_per_cpu_kthreads

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There is a recursive lock on the cpu_hotplug_lock.

In kernel/trace/trace_osnoise.c:<start/stop>_per_cpu_kthreads:
    - start_per_cpu_kthreads calls cpus_read_lock() and if
	start_kthreads returns a error it will call stop_per_cpu_kthreads.
    - stop_per_cpu_kthreads then calls cpus_read_lock() again causing
      deadlock.

Fix this by calling cpus_read_unlock() before calling
stop_per_cpu_kthreads. This behavior can also be seen in commit
f46b16520a ("trace/hwlat: Implement the per-cpu mode").

This error was noticed during the LTP ftrace-stress-test:

WARNING: possible recursive locking detected
--------------------------------------------
sh/275006 is trying to acquire lock:
ffffffffb02f5400 (cpu_hotplug_lock){++++}-{0:0}, at: stop_per_cpu_kthreads

but task is already holding lock:
ffffffffb02f5400 (cpu_hotplug_lock){++++}-{0:0}, at: start_per_cpu_kthreads

other info that might help us debug this:
 Possible unsafe locking scenario:

      CPU0
      ----
 lock(cpu_hotplug_lock);
 lock(cpu_hotplug_lock);

 *** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by sh/275006:
 #0: ffff8881023f0470 (sb_writers#24){.+.+}-{0:0}, at: ksys_write
 #1: ffffffffb084f430 (trace_types_lock){+.+.}-{3:3}, at: rb_simple_write
 #2: ffffffffb02f5400 (cpu_hotplug_lock){++++}-{0:0}, at: start_per_cpu_kthreads

Link: https://lkml.kernel.org/r/20220919144932.3064014-1-npache@redhat.com

Fixes: c8895e271f ("trace/osnoise: Support hotplug operations")
Signed-off-by: Nico Pache <npache@redhat.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Nico Pache 2022-09-19 08:49:32 -06:00 committed by Steven Rostedt (Google)
parent d8ef45d66c
commit 99ee9317a1
1 changed files with 2 additions and 1 deletions
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3
kernel/trace/trace_osnoise.c
View file

@ -1786,8 +1786,9 @@ static int start_per_cpu_kthreads(void)
for_each_cpu(cpu, current_mask) {
retval = start_kthread(cpu);
if (retval) {
cpus_read_unlock();
stop_per_cpu_kthreads();
break;
return retval;
}
}