From: Xiaoguang Wang xiaoguang.wang@linux.alibaba.com
[ 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@syzkaller.appspotmail.com Signed-off-by: Xiaoguang Wang xiaoguang.wang@linux.alibaba.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- 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 9690c845a3e4b..01f71b9efb88f 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6451,7 +6451,7 @@ 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);