From c57a91fb1ccfa203ba3e31e5a389cb04de5b0561 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Wed, 8 Sep 2021 20:49:17 +0100 Subject: [PATCH] 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 Link: https://lore.kernel.org/r/2982e53bcea2274006ed435ee2a77197107d8a29.1631130542.git.asml.silence@gmail.com Signed-off-by: Jens Axboe --- fs/io_uring.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index d816c09c88a5..d80d8359501f 100644 --- 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))