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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
	Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>,
	linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org
Subject: [PATCH AUTOSEL 5.6 45/50] io_uring: use cond_resched() in io_ring_ctx_wait_and_kill()
Date: Thu,  7 May 2020 10:27:21 -0400	[thread overview]
Message-ID: <20200507142726.25751-45-sashal@kernel.org> (raw)
In-Reply-To: <20200507142726.25751-1-sashal@kernel.org>

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 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


      parent reply	other threads:[~2020-05-07 14:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200507142726.25751-1-sashal@kernel.org>
2020-05-07 14:27 ` [PATCH AUTOSEL 5.6 38/50] Fix use after free in get_tree_bdev() Sasha Levin
2020-05-07 14:27 ` [PATCH AUTOSEL 5.6 42/50] fibmap: Warn and return an error in case of block > INT_MAX Sasha Levin
2020-05-07 14:27 ` Sasha Levin [this message]

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