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From: Sasha Levin <[email protected]>
To: [email protected], [email protected]
Cc: Xiaoguang Wang <[email protected]>,
	Jens Axboe <[email protected]>, Sasha Levin <[email protected]>,
	[email protected], [email protected]
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: <[email protected]> (raw)
In-Reply-To: <[email protected]>

From: Xiaoguang Wang <[email protected]>

[ 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: [email protected]
Signed-off-by: Xiaoguang Wang <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
 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


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

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