From: "Stefan Bühler" <source@stbuehler.de>
To: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH v1 2/3] io_uring: fix race condition when sq threads goes sleeping
Date: Fri, 19 Apr 2019 11:57:45 +0200 [thread overview]
Message-ID: <20190419095746.22894-2-source@stbuehler.de> (raw)
In-Reply-To: <20190419095746.22894-1-source@stbuehler.de>
Reading the SQ tail needs to come after setting IORING_SQ_NEED_WAKEUP in
flags; there is no cheap barrier for ordering a store before a load, a
full memory barrier is required.
Userspace needs a full memory barrier between updating SQ tail and
checking for the IORING_SQ_NEED_WAKEUP too.
Signed-off-by: Stefan Bühler <source@stbuehler.de>
---
fs/io_uring.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 96863e4780b7..912b0b304d90 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1865,7 +1865,8 @@ static int io_sq_thread(void *data)
/* Tell userspace we may need a wakeup call */
ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
- smp_wmb();
+ /* make sure to read SQ tail after writing flags */
+ smp_mb();
if (!io_get_sqring(ctx, &sqes[0])) {
if (kthread_should_stop()) {
--
2.20.1
next prev parent reply other threads:[~2019-04-19 18:49 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-14 16:44 io_uring memory ordering (and broken queue-is-full checks) Stefan Bühler
2019-04-17 15:02 ` Jens Axboe
2019-04-19 9:29 ` Stefan Bühler
2019-04-19 9:57 ` [PATCH v1 1/3] io_uring: fix race condition reading SQ entries Stefan Bühler
2019-04-19 9:57 ` Stefan Bühler [this message]
2019-04-19 9:57 ` [PATCH v1 3/3] io_uring: fix poll full SQ detection Stefan Bühler
2019-04-22 17:04 ` io_uring memory ordering (and broken queue-is-full checks) Jens Axboe
2019-04-24 21:54 ` [PATCH barrier cleanup v1 1/7] io_uring: fix notes on barriers Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 2/7] io_uring: remove unnecessary barrier before wq_has_sleeper Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 3/7] io_uring: remove unnecessary barrier before reading cq head Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 4/7] io_uring: remove unnecessary barrier after updating SQ head Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 5/7] io_uring: remove unnecessary barrier before reading SQ tail Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 6/7] io_uring: remove unnecessary barrier after incrementing dropped counter Stefan Bühler
2019-04-24 21:54 ` [PATCH barrier cleanup v1 7/7] io_uring: remove unnecessary barrier after unsetting IORING_SQ_NEED_WAKEUP Stefan Bühler
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