io_uring: ensure deferred completions are posted for multishot

Commit 687b2bae0efff9b25e071737d6af5004e6e35af5 upstream.

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,
and cause confusion on the application side.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 488793b119d0cad4f1618a9c34fe1984805dd664..f39d66589180e582ee176404f3154d0272a35939 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -819,6 +819,14 @@ bool io_post_aux_cqe(struct io_ring_ctx *ctx,
 {
        bool filled;
 
+       /*
+        * 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);
+
        io_cq_lock(ctx);
        filled = io_fill_cqe_aux(ctx, user_data, res, cflags, allow_overflow);
        io_cq_unlock_post(ctx);