The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 4aa84f2ffa81f71e15e5cffc2cc6090dbee78f8e Mon Sep 17 00:00:00 2001
From: Pavel Begunkov asml.silence@gmail.com Date: Thu, 7 Jan 2021 03:15:42 +0000 Subject: [PATCH] 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
diff --git a/fs/io_uring.c b/fs/io_uring.c index 91e517ad1421..401316fe2ae2 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1345,11 +1345,6 @@ 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) @@ -1711,6 +1706,10 @@ static void io_cqring_ev_posted(struct io_ring_ctx *ctx) wake_up(&ctx->sq_data->wait); if (io_should_trigger_evfd(ctx)) eventfd_signal(ctx->cq_ev_fd, 1); + if (wq_has_sleeper(&ctx->cq_wait)) { + wake_up_interruptible(&ctx->cq_wait); + kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN); + } }
static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx) @@ -1721,6 +1720,10 @@ static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx) } if (io_should_trigger_evfd(ctx)) eventfd_signal(ctx->cq_ev_fd, 1); + if (wq_has_sleeper(&ctx->cq_wait)) { + wake_up_interruptible(&ctx->cq_wait); + kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN); + } }
/* Returns true if there are no backlogged entries after the flush */