io_uring: synchronise ev_posted() with waitqueues

waitqueue_active() needs smp_mb() to be in sync with waitqueues
modification, but we miss it in io_cqring_ev_posted*() apart from
cq_wait() case.

Take an smb_mb() out of wq_has_sleeper() making it waitqueue_active(),
and place it a few lines before, so it can synchronise other
waitqueue_active() as well.

The patch doesn't add any additional overhead, so even if there are
no problems currently, it's just safer to have it this way.

Signed-off-by: Pavel Begunkov <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 401316f..cb57e03 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1700,13 +1700,16 @@ static inline unsigned __io_cqring_events(struct io_ring_ctx *ctx)
 
 static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
 {
+       /* see waitqueue_active() comment */
+       smp_mb();
+
        if (waitqueue_active(&ctx->wait))
                wake_up(&ctx->wait);
        if (ctx->sq_data && waitqueue_active(&ctx->sq_data->wait))
                wake_up(&ctx->sq_data->wait);
        if (io_should_trigger_evfd(ctx))
                eventfd_signal(ctx->cq_ev_fd, 1);
-       if (wq_has_sleeper(&ctx->cq_wait)) {
+       if (waitqueue_active(&ctx->cq_wait)) {
                wake_up_interruptible(&ctx->cq_wait);
                kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
        }
@@ -1714,13 +1717,16 @@ 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 (waitqueue_active(&ctx->wait))
                        wake_up(&ctx->wait);
        }
        if (io_should_trigger_evfd(ctx))
                eventfd_signal(ctx->cq_ev_fd, 1);
-       if (wq_has_sleeper(&ctx->cq_wait)) {
+       if (waitqueue_active(&ctx->cq_wait)) {
                wake_up_interruptible(&ctx->cq_wait);
                kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
        }