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io_uring: dont kill fasync under completion_lock

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[ Upstream commit 4aa84f2ffa81f71e15e5cffc2cc6090dbee78f8e ]

      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).

Cc: stable@vger.kernel.org # 5.5+
Reported-by: syzbot+91ca3f25bd7f795f019c@syzkaller.appspotmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pavel Begunkov 2021-01-26 11:17:09 +00:00 committed by Greg Kroah-Hartman
parent 186725a80c
commit 7bccd1c191
1 changed files with 4 additions and 5 deletions
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9
fs/io_uring.c
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@ -1214,11 +1214,6 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
/* order cqe stores with ring update */
smp_store_release(&rings->cq.tail, ctx->cached_cq_tail);
if (wq_has_sleeper(&ctx->cq_wait)) {
wake_up_interruptible(&ctx->cq_wait);
kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
}
}
static void io_put_identity(struct io_uring_task *tctx, struct io_kiocb *req)
@ -1604,6 +1599,10 @@ static inline bool io_should_trigger_evfd(struct io_ring_ctx *ctx)
static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
{
if (wq_has_sleeper(&ctx->cq_wait)) {
wake_up_interruptible(&ctx->cq_wait);
kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
}
if (waitqueue_active(&ctx->wait))
wake_up(&ctx->wait);
if (ctx->sq_data && waitqueue_active(&ctx->sq_data->wait))