net: linkwatch: use system_unbound_wq

linkwatch_event() grabs possibly very contended RTNL mutex.

system_wq is not suitable for such work.

Inspired by many noisy syzbot reports.

3 locks held by kworker/0:7/5266:
 #0: ffff888015480948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3206 [inline]
 #0: ffff888015480948 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
 #1: ffffc90003f6fd00 ((linkwatch_work).work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3207 [inline]
 , at: process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
 #2: ffffffff8fa6f208 (rtnl_mutex){+.+.}-{3:3}, at: linkwatch_event+0xe/0x60 net/core/link_watch.c:276

Reported-by: syzbot <syzkaller@googlegroups.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20240805085821.1616528-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/link_watch.c b/net/core/link_watch.c
index 8ec35194bfcb8574f53a9fd28f0cb2ebfe9a3f2e..ab150641142aa1545c71fc5d3b11db33c70cf437 100644 (file)
--- a/net/core/link_watch.c
+++ b/net/core/link_watch.c
@@ -148,9 +148,9 @@ static void linkwatch_schedule_work(int urgent)
         * override the existing timer.
         */
        if (test_bit(LW_URGENT, &linkwatch_flags))
-               mod_delayed_work(system_wq, &linkwatch_work, 0);
+               mod_delayed_work(system_unbound_wq, &linkwatch_work, 0);
        else
-               schedule_delayed_work(&linkwatch_work, delay);
+               queue_delayed_work(system_unbound_wq, &linkwatch_work, delay);
 }