Messages in this thread Patch in this message | | | From | Nico Pache <> | Subject | [PATCH] trace/osnoise: Fix possible recursive locking in stop_per_cpu_kthreads | Date | Mon, 19 Sep 2022 08:49:32 -0600 |
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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 f46b16520a08 ("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
Fixes: c8895e271f79 ("trace/osnoise: Support hotplug operations") Signed-off-by: Nico Pache <npache@redhat.com> --- kernel/trace/trace_osnoise.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index 313439920a8c..78d536d3ff3d 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -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; } } -- 2.37.2
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