io_uring: never overflow io_aux_cqe

Now all callers of io_aux_cqe() set allow_overflow to false, remove the
parameter and not allow overflowing auxilary multishot cqes.

When CQ is full the function callers and all multishot requests in
general are expected to complete the request. That prevents indefinite
in-background grows of the overflow list and let's the userspace to
handle the backlog at its own pace.

Resubmitting a request should also be faster than accounting a bunch of
overflows, so it should be better for perf when it happens, but a well
behaving userspace should be trying to avoid overflows in any case.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/bb20d14d708ea174721e58bb53786b0521e4dd6d.1691757663.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 4 deletions

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 7595658a5073a..e57d00939ab9c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -939,15 +939,18 @@ bool io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags
 	return __io_post_aux_cqe(ctx, user_data, res, cflags, true);
 }
 
-bool io_aux_cqe(const struct io_kiocb *req, bool defer, s32 res, u32 cflags,
-		bool allow_overflow)
+/*
+ * A helper for multishot requests posting additional CQEs.
+ * Should only be used from a task_work including IO_URING_F_MULTISHOT.
+ */
+bool io_fill_cqe_req_aux(struct io_kiocb *req, bool defer, s32 res, u32 cflags)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	u64 user_data = req->cqe.user_data;
 	struct io_uring_cqe *cqe;
 
 	if (!defer)
-		return __io_post_aux_cqe(ctx, user_data, res, cflags, allow_overflow);
+		return __io_post_aux_cqe(ctx, user_data, res, cflags, false);
 
 	lockdep_assert_held(&ctx->uring_lock);
 
@@ -962,7 +965,7 @@ bool io_aux_cqe(const struct io_kiocb *req, bool defer, s32 res, u32 cflags,
 	 * however it's main job is to prevent unbounded posted completions,
 	 * and in that it works just as well.
 	 */
-	if (!allow_overflow && test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
+	if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
 		return false;
 
 	cqe = &ctx->submit_state.cqes[ctx->submit_state.cqes_count++];