Commit 8f487ef2 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

io_uring: mitigate unlikely iopoll lag 



We have requests like IORING_OP_FILES_UPDATE that don't go through
->iopoll_list but get completed in place under ->uring_lock, and so
after dropping the lock io_iopoll_check() should expect that some CQEs
might have get completed in a meanwhile.

Currently such events won't be accounted in @nr_events, and the loop
will continue to poll even if there is enough of CQEs. It shouldn't be a
problem as it's not likely to happen and so, but not nice either. Just
return earlier in this case, it should be enough.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/66ef932cc66a34e3771bbae04b2953a8058e9d05.1625747741.git.asml.silence@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent c32aace0

fs/io_uring.c

+5 −1
Original line number Diff line number Diff line
@@ -2356,11 +2356,15 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min) 
		 * very same mutex.

		 */

		if (list_empty(&ctx->iopoll_list)) {

			u32 tail = ctx->cached_cq_tail;



			mutex_unlock(&ctx->uring_lock);

			io_run_task_work();

			mutex_lock(&ctx->uring_lock);



			if (list_empty(&ctx->iopoll_list))

			/* some requests don't go through iopoll_list */

			if (tail != ctx->cached_cq_tail ||

			    list_empty(&ctx->iopoll_list))

				break;

		}

		ret = io_do_iopoll(ctx, &nr_events, min);