io_uring: fix __io_iopoll_check deadlock in io_sq_thread (c7849be9) · Commits · 戴 / test

Since commit ("io_uring: don't enter poll loop if we have CQEs pending"), if we already events pending, we won't enter poll loop. In case SETUP_IOPOLL and SETUP_SQPOLL are both enabled, if app has been terminated and don't reap pending events which are already in cq ring, and there are some reqs in poll_list, io_sq_thread will enter __io_iopoll_check(), and find pending events, then return, this loop will never have a chance to exit. I have seen this issue in fio stress tests, to fix this issue, let io_sq_thread call io_iopoll_getevents() with argument 'min' being zero, and remove __io_iopoll_check(). Fixes: ("io_uring: don't enter poll loop if we have CQEs pending") Signed-off-by:

Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

+9 −18

Original line number	Diff line number	Diff line
		@@ -1672,11 +1672,17 @@ static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
		mutex_unlock(&ctx->uring_lock);
		}

		static int __io_iopoll_check(struct io_ring_ctx ctx, unsigned nr_events,
		static int io_iopoll_check(struct io_ring_ctx ctx, unsigned nr_events,
		long min)
		{
		int iters = 0, ret = 0;

		/*
		* We disallow the app entering submit/complete with polling, but we
		* still need to lock the ring to prevent racing with polled issue
		* that got punted to a workqueue.
		*/
		mutex_lock(&ctx->uring_lock);
		do {
		int tmin = 0;

		@@ -1712,21 +1718,6 @@ static int __io_iopoll_check(struct io_ring_ctx ctx, unsigned nr_events,
		ret = 0;
		} while (min && !*nr_events && !need_resched());

		return ret;
		}

		static int io_iopoll_check(struct io_ring_ctx ctx, unsigned nr_events,
		long min)
		{
		int ret;

		/*
		* We disallow the app entering submit/complete with polling, but we
		* still need to lock the ring to prevent racing with polled issue
		* that got punted to a workqueue.
		*/
		mutex_lock(&ctx->uring_lock);
		ret = __io_iopoll_check(ctx, nr_events, min);
		mutex_unlock(&ctx->uring_lock);
		return ret;
		}
		@@ -5118,7 +5109,7 @@ static int io_sq_thread(void *data)
		*/
		mutex_lock(&ctx->uring_lock);
		if (!list_empty(&ctx->poll_list))
		__io_iopoll_check(ctx, &nr_events, 0);
		io_iopoll_getevents(ctx, &nr_events, 0);
		else
		inflight = 0;
		mutex_unlock(&ctx->uring_lock);

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