[PATCH 5.19 527/717] tracing/osnoise: Fix possible recursive locking in stop_per_cpu_kthreads

Greg Kroah-Hartman
2022-10-22T08:47:19Z

From: Nico Pache <npache@redhat.com>

[ Upstream commit 99ee9317a1305cd5626736785c8cb38b0e47686c ]

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

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

Fixes: c8895e271f79 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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;
}
}

--
2.35.1