6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
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, 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -884,6 +884,14 @@ bool io_req_post_cqe(struct io_kiocb *re 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);