[PATCH v2] tracing: Fix crash passing ERR_PTR to kthread_stop()

event_test_stuff() calls kthread_run() and unconditionally passes the
returned task_struct pointer to kthread_stop(). kthread_run() returns an
error pointer such as ERR_PTR(-ENOMEM) when kthread creation fails, for
example under memory pressure during the boot-time event self-test.
kthread_stop() then dereferences the invalid pointer, crashing the kernel.

Check the result of kthread_run() before passing it to kthread_stop(). Use
WARN_ON() so that a failure to create the self-test thread does not go
unnoticed, matching the ring-buffer self-test fix in commit
91542863abad ("ring-buffer: Fix crash passing ERR_PTR to kthread_stop()").

Fixes: e6187007d6c3 ("tracing/events: add startup tests for events")
Cc: [email protected]
Signed-off-by: Hui Su <[email protected]>
---

Changes in v2:
- Use WARN_ON(IS_ERR(test_thread)) so thread creation failures are not
  silently ignored, as suggested by Steven Rostedt.

v1: https://lore.kernel.org/r/[email protected]/

 kernel/trace/trace_events.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 3650d84d4f16..28167b229419 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -4901,6 +4901,8 @@ static __init void event_test_stuff(void)
 	struct task_struct *test_thread;
 
 	test_thread = kthread_run(event_test_thread, NULL, "test-events");
+	if (WARN_ON(IS_ERR(test_thread)))
+		return;
 	msleep(1);
 	kthread_stop(test_thread);
 }
-- 
2.54.0