From 3fd44c86711f71156b586c22b0495c58f69358bb Mon Sep 17 00:00:00 2001 From: Xiaoguang Wang Date: Fri, 1 May 2020 08:52:56 +0800 Subject: [PATCH] io_uring: use cond_resched() in io_ring_ctx_wait_and_kill() 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 Signed-off-by: Jens Axboe --- 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 3da2a02531e6..5ca2da6648d0 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -7343,7 +7343,7 @@ 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