From: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
[ Upstream commit 3fd44c86711f71156b586c22b0495c58f69358bb ]
While working on to make io_uring sqpoll mode support syscalls that need
struct files_struct, I got cpu soft lockup in io_ring_ctx_wait_and_kill(),
while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait))
cpu_relax();
above loop never has an chance to exit, it's because preempt isn't enabled
in the kernel, and the context calling io_ring_ctx_wait_and_kill() and
io_sq_thread() run in the same cpu, if io_sq_thread calls a cond_resched()
yield cpu and another context enters above loop, then io_sq_thread() will
always in runqueue and never exit.
Use cond_resched() can fix this issue.
Reported-by: syzbot+66243bb7126c410cefe6@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/io_uring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index a46de2cfc28e8..b5ade01379029 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6449,7 +6449,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
* it could cause shutdown to hang.
*/
while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait))
- cpu_relax();
+ cond_resched();
io_kill_timeouts(ctx);
io_poll_remove_all(ctx);
--
2.20.1
