linux-kernel - Re: [syzbot] [fs?] WARNING: bad unlock balance in seq_read

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Message-ID: <tencent_C95D9CDDB01966CFA00DC1A5898D84920707@qq.com>
Date: Sat,  1 Feb 2025 13:30:01 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+c041985778e4069e1ce3@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] WARNING: bad unlock balance in seq_read_iter

#syz test

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 4cb275316e51..dad032912e1e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1600,11 +1600,12 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 	struct set_event_iter *iter;
 	loff_t l;
 
+	mutex_lock(&event_mutex);
+
 	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
-	if (!iter)
+	if (!iter) {
 		return NULL;
-
-	mutex_lock(&event_mutex);
+	}
 
 	iter->type = SET_EVENT_FILE;
 	iter->file = list_entry(&tr->events, struct trace_event_file, list);