From c57a91fb1ccfa203ba3e31e5a389cb04de5b0561 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Wed, 8 Sep 2021 20:49:17 +0100
Subject: [PATCH] io_uring: fix missing mb() before waitqueue_active
Git-commit: c57a91fb1ccfa203ba3e31e5a389cb04de5b0561
Patch-mainline: v5.15-rc1
References: git-fixes
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>
Link: https://lore.kernel.org/r/2982e53bcea2274006ed435ee2a77197107d8a29.1631130542.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
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))
--
2.35.3