[PATCH AUTOSEL 5.7 39/53] io_uring: fix io_sq_thread no schedule when busy

Sasha Levin
2020-07-02T01:25:28Z

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

[ 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@kernel.dk>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1829be7f63a35..6cf9d509371e2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6071,7 +6071,7 @@ 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
@@ -6087,7 +6087,7 @@ 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)
--
2.25.1