This is a note to let you know that I've just added the patch titled io_uring: fix io_sq_thread no schedule when busy to the 5.7-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: io_uring-fix-io_sq_thread-no-schedule-when-busy.patch and it can be found in the queue-5.7 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 4facbc6278d7946f8f884a73a288270194e98c6c Author: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> Date: Tue Jun 23 19:34:06 2020 +0800 io_uring: fix io_sq_thread no schedule when busy [ Upstream commit b772f07add1c0b22e02c0f1e96f647560679d3a9 ] When the user consumes and generates sqe at a fast rate, io_sqring_entries can always get sqe, and ret will not be equal to -EBUSY, so that io_sq_thread will never call cond_resched or schedule, and then we will get the following system error prompt: rcu: INFO: rcu_sched self-detected stall on CPU or watchdog: BUG: soft lockup-CPU#23 stuck for 112s! [io_uring-sq:1863] This patch checks whether need to call cond_resched() by checking the need_resched() function every cycle. Suggested-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/io_uring.c b/fs/io_uring.c index bb74e45941af2..63a456921903e 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6084,7 +6084,7 @@ static int io_sq_thread(void *data) * If submit got -EBUSY, flag us as needing the application * to enter the kernel to reap and flush events. */ - if (!to_submit || ret == -EBUSY) { + if (!to_submit || ret == -EBUSY || need_resched()) { /* * Drop cur_mm before scheduling, we can't hold it for * long periods (or over schedule()). Do this before @@ -6100,7 +6100,7 @@ static int io_sq_thread(void *data) * more IO, we should wait for the application to * reap events and wake us up. */ - if (!list_empty(&ctx->poll_list) || + if (!list_empty(&ctx->poll_list) || need_resched() || (!time_after(jiffies, timeout) && ret != -EBUSY && !percpu_ref_is_dying(&ctx->refs))) { if (current->task_works)