From: Sasha Levin Date: Mon, 29 Sep 2025 11:32:38 +0000 (-0400) Subject: tracing: Fix lock imbalance in s_start() memory allocation failure path X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=61e19cd2e5c5235326a13a68df1a2f8ec4eeed7b;p=thirdparty%2Fkernel%2Fstable.git tracing: Fix lock imbalance in s_start() memory allocation failure path When s_start() fails to allocate memory for set_event_iter, it returns NULL before acquiring event_mutex. However, the corresponding s_stop() function always tries to unlock the mutex, causing a lock imbalance warning: WARNING: bad unlock balance detected! 6.17.0-rc7-00175-g2b2e0c04f78c #7 Not tainted ------------------------------------- syz.0.85611/376514 is trying to release lock (event_mutex) at: [] traverse.part.0.constprop.0+0x2c4/0x650 fs/seq_file.c:131 but there are no more locks to release! The issue was introduced by commit b355247df104 ("tracing: Cache ':mod:' events for modules not loaded yet") which added the kzalloc() allocation before the mutex lock, creating a path where s_start() could return without locking the mutex while s_stop() would still try to unlock it. Fix this by unconditionally acquiring the mutex immediately after allocation, regardless of whether the allocation succeeded. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/20250929113238.3722055-1-sashal@kernel.org Fixes: b355247df104 ("tracing: Cache ":mod:" events for modules not loaded yet") Signed-off-by: Sasha Levin Signed-off-by: Steven Rostedt (Google) --- diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 9f3e9537417d5..e00da4182deb7 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1629,11 +1629,10 @@ static void *s_start(struct seq_file *m, loff_t *pos) loff_t l; iter = kzalloc(sizeof(*iter), GFP_KERNEL); + mutex_lock(&event_mutex); if (!iter) return NULL; - mutex_lock(&event_mutex); - iter->type = SET_EVENT_FILE; iter->file = list_entry(&tr->events, struct trace_event_file, list);