io_uring: fix missing mb() before waitqueue_active

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>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d816c09c88a544a271ba192cf9f143d23577002f..d80d8359501faebb321ff54665645fd48b9370de 100644 (file)
--- 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))