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@xxxxxxxxxxxx>
---
fs/io_uring.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7025e9830abe..1f4419f38ef1 100644
--- 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);
@@ -2674,7 +2668,9 @@ 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)
--
2.20.1
