Commit c07e6719 authored Dec 14, 2020 by Xiaoguang Wang Committed by Jens Axboe Dec 22, 2020

io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work()



io_iopoll_complete() does not hold completion_lock to complete polled io,
so in io_wq_submit_work(), we can not call io_req_complete() directly, to
complete polled io, otherwise there maybe concurrent access to cqring,
defer_list, etc, which is not safe. Commit dad1b124 ("io_uring: always
let io_iopoll_complete() complete polled io") has fixed this issue, but
Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is not
good.

Given that io_iopoll_complete() is always called under uring_lock, so here
for polled io, we can also get uring_lock to fix this issue.

Fixes: dad1b124 ("io_uring: always let io_iopoll_complete() complete polled io")
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: don't deref 'req' after completing it']
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 9faadcc8

fs/io_uring.c

+19 −10

Original line number	Diff line number	Diff line
		@@ -6332,19 +6332,28 @@ static struct io_wq_work io_wq_submit_work(struct io_wq_work work)
		}

		if (ret) {
		struct io_ring_ctx *lock_ctx = NULL;

		if (req->ctx->flags & IORING_SETUP_IOPOLL)
		lock_ctx = req->ctx;

		/*
		* io_iopoll_complete() does not hold completion_lock to complete
		* polled io, so here for polled io, just mark it done and still let
		* io_iopoll_complete() complete it.
		* io_iopoll_complete() does not hold completion_lock to
		* complete polled io, so here for polled io, we can not call
		* io_req_complete() directly, otherwise there maybe concurrent
		* access to cqring, defer_list, etc, which is not safe. Given
		* that io_iopoll_complete() is always called under uring_lock,
		* so here for polled io, we also get uring_lock to complete
		* it.
		*/
		if (req->ctx->flags & IORING_SETUP_IOPOLL) {
		struct kiocb *kiocb = &req->rw.kiocb;
		if (lock_ctx)
		mutex_lock(&lock_ctx->uring_lock);

		kiocb_done(kiocb, ret, NULL);
		} else {
		req_set_fail_links(req);
		io_req_complete(req, ret);
		}

		if (lock_ctx)
		mutex_unlock(&lock_ctx->uring_lock);
		}

		return io_steal_work(req);

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