[PATCH 3/5] io_uring_poll: kill the no longer necessary barrier after poll_wait()

Oleg Nesterov
2025-01-07T16:28:08Z

Now that poll_wait() provides a full barrier we can remove smp_rmb() from
io_uring_poll().

In fact I don't think smp_rmb() was correct, it can't serialize LOADs and
STOREs.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
io_uring/io_uring.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 06ff41484e29..a64a82b93b86 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2809,13 +2809,12 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)

if (unlikely(!ctx->poll_activated))
io_activate_pollwq(ctx);
-
- poll_wait(file, &ctx->poll_wq, wait);
/*
- * synchronizes with barrier from wq_has_sleeper call in
- * io_commit_cqring
+ * provides mb() which pairs with barrier from wq_has_sleeper
+ * call in io_commit_cqring
*/
- smp_rmb();
+ poll_wait(file, &ctx->poll_wq, wait);
+
if (!io_sqring_full(ctx))
mask |= EPOLLOUT | EPOLLWRNORM;

--
2.25.1.362.g51ebf55