Commit b772f07a authored Jun 23, 2020 by Xuan Zhuo Committed by Jens Axboe Jun 23, 2020

io_uring: fix io_sq_thread no schedule when busy



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@kernel.dk>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 48778464

fs/io_uring.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -6011,7 +6011,7 @@ 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
		@@ -6027,7 +6027,7 @@ 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)

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