io_uring: dont kill fasync under completion_lock
authorPavel Begunkov <asml.silence@gmail.com>
Thu, 7 Jan 2021 03:15:42 +0000 (03:15 +0000)
committerJens Axboe <axboe@kernel.dk>
Thu, 7 Jan 2021 14:48:09 +0000 (07:48 -0700)
commit4aa84f2ffa81f71e15e5cffc2cc6090dbee78f8e
tree4c907bc09f6231c0a4ea89092800bad04347272f
parent80c18e4ac20c9cde420cb3ffab48c936147cf07d
io_uring: dont kill fasync under completion_lock

      CPU0                    CPU1
       ----                    ----
  lock(&new->fa_lock);
                               local_irq_disable();
                               lock(&ctx->completion_lock);
                               lock(&new->fa_lock);
  <Interrupt>
    lock(&ctx->completion_lock);

 *** DEADLOCK ***

Move kill_fasync() out of io_commit_cqring() to io_cqring_ev_posted(),
so it doesn't hold completion_lock while doing it. That saves from the
reported deadlock, and it's just nice to shorten the locking time and
untangle nested locks (compl_lock -> wq_head::lock).

Reported-by: syzbot+91ca3f25bd7f795f019c@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
fs/io_uring.c