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From: Pavel Begunkov <asml.silence@gmail.com>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Subject: [PATCH 1/1] io_uring: fix missing mb() before waitqueue_active
Date: Wed,  8 Sep 2021 20:49:17 +0100	[thread overview]
Message-ID: <2982e53bcea2274006ed435ee2a77197107d8a29.1631130542.git.asml.silence@gmail.com> (raw)

In case of !SQPOLL, io_cqring_ev_posted_iopoll() doesn't provide a
memory barrier required by waitqueue_active(&ctx->poll_wait). There is
a wq_has_sleeper(), which does smb_mb() inside, but it's called only for
SQPOLL.

Fixes: 5fd4617840596 ("io_uring: be smarter about waking multiple CQ ring waiters")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d816c09c88a5..d80d8359501f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1619,8 +1619,11 @@ static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
 
 static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
 {
+	/* see waitqueue_active() comment */
+	smp_mb();
+
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
-		if (wq_has_sleeper(&ctx->cq_wait))
+		if (waitqueue_active(&ctx->cq_wait))
 			wake_up_all(&ctx->cq_wait);
 	}
 	if (io_should_trigger_evfd(ctx))
-- 
2.33.0


             reply	other threads:[~2021-09-08 19:50 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-08 19:49 Pavel Begunkov [this message]
2021-09-08 19:57 ` [PATCH 1/1] io_uring: fix missing mb() before waitqueue_active Jens Axboe
2021-09-08 20:09   ` Pavel Begunkov
2021-09-08 20:15     ` Jens Axboe
2021-09-08 20:22       ` Pavel Begunkov
2021-09-08 20:24         ` Jens Axboe

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