The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 687b2bae0efff9b25e071737d6af5004e6e35af5 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025051212-antirust-outshoot-07f7@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 687b2bae0efff9b25e071737d6af5004e6e35af5 Mon Sep 17 00:00:00 2001 From: Jens Axboe axboe@kernel.dk Date: Wed, 7 May 2025 07:34:24 -0600 Subject: [PATCH] io_uring: ensure deferred completions are flushed for multishot

Multishot normally uses io_req_post_cqe() to post completions, but when stopping it, it may finish up with a deferred completion. This is fine, except if another multishot event triggers before the deferred completions get flushed. If this occurs, then CQEs may get reordered in the CQ ring, as new multishot completions get posted before the deferred ones are flushed. This can cause confusion on the application side, if strict ordering is required for the use case.

When multishot posting via io_req_post_cqe(), flush any pending deferred completions first, if any.

Cc: stable@vger.kernel.org # 6.1+ Reported-by: Norman Maurer norman_maurer@apple.com Reported-by: Christian Mazakas christian.mazakas@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 769814d71153..541e65a1eebf 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -848,6 +848,14 @@ bool io_req_post_cqe(struct io_kiocb *req, s32 res, u32 cflags) struct io_ring_ctx *ctx = req->ctx; bool posted;

+ /* + * If multishot has already posted deferred completions, ensure that + * those are flushed first before posting this one. If not, CQEs + * could get reordered. + */ + if (!wq_list_empty(&ctx->submit_state.compl_reqs)) + __io_submit_flush_completions(ctx); + lockdep_assert(!io_wq_current_is_worker()); lockdep_assert_held(&ctx->uring_lock);