io_uring: remove unnecessary barrier before wq_has_sleeper

wq_has_sleeper has a full barrier internally. The smp_rmb barrier in
io_uring_poll synchronizes with it.

Signed-off-by: Stefan Bühler <source@stbuehler.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7ab93e854eb21e04c0f4c745886cf85a14a32d4f..bb71b7f00bb388bca3f293b1c8587a436a62b277 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -418,12 +418,6 @@ static void io_commit_cqring(struct io_ring_ctx *ctx)
                /* order cqe stores with ring update */
                smp_store_release(&ring->r.tail, ctx->cached_cq_tail);
 
-               /*
-                * Write sider barrier of tail update, app has read side. See
-                * comment at the top of this file.
-                */
-               smp_wmb();
-
                if (wq_has_sleeper(&ctx->cq_wait)) {
                        wake_up_interruptible(&ctx->cq_wait);
                        kill_fasync(&ctx->cq_fasync, SIGIO, POLL_IN);
@@ -2677,7 +2671,10 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
        __poll_t mask = 0;
 
        poll_wait(file, &ctx->cq_wait, wait);
-       /* See comment at the top of this file */
+       /*
+        * synchronizes with barrier from wq_has_sleeper call in
+        * io_commit_cqring
+        */
        smp_rmb();
        if (READ_ONCE(ctx->sq_ring->r.tail) - ctx->cached_sq_head !=
            ctx->sq_ring->ring_entries)