io_uring: briefly loose locks while reaping events

It's not nice to hold @uring_lock for too long io_iopoll_reap_events().
For instance, the lock is needed to publish requests to @poll_list, and
that locks out tasks doing that for no good reason. Loose it
occasionally.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2069,8 +2069,13 @@ static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
 		/*
 		 * Ensure we allow local-to-the-cpu processing to take place,
 		 * in this case we need to ensure that we reap all events.
+		 * Also let task_work, etc. to progress by releasing the mutex
 		 */
-		cond_resched();
+		if (need_resched()) {
+			mutex_unlock(&ctx->uring_lock);
+			cond_resched();
+			mutex_lock(&ctx->uring_lock);
+		}
 	}
 	mutex_unlock(&ctx->uring_lock);
 }