io_uring/napi: ensure napi polling is aborted when work is available

While testing io_uring NAPI with DEFER_TASKRUN, I ran into slowdowns and
stalls in packet delivery. Turns out that while
io_napi_busy_loop_should_end() aborts appropriately on regular
task_work, it does not abort if we have local task_work pending.

Move io_has_work() into the private io_uring.h header, and gate whether
we should continue polling on that as well. This makes NAPI polling on
send/receive work as designed with IORING_SETUP_DEFER_TASKRUN as well.

Fixes: 8d0c12a ("io-uring: add napi busy poll support")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/io_uring.c

@@ -122,11 +122,6 @@
 #define IO_COMPL_BATCH			32
 #define IO_REQ_ALLOC_BATCH		8
 
-enum {
-	IO_CHECK_CQ_OVERFLOW_BIT,
-	IO_CHECK_CQ_DROPPED_BIT,
-};
-
 struct io_defer_entry {
 	struct list_head	list;
 	struct io_kiocb		*req;
@@ -2479,12 +2474,6 @@ int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
 	return ret;
 }
 
-static inline bool io_has_work(struct io_ring_ctx *ctx)
-{
-	return test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq) ||
-	       !llist_empty(&ctx->work_llist);
-}
-
 static int io_wake_function(struct wait_queue_entry *curr, unsigned int mode,
 			    int wake_flags, void *key)
 {

io_uring/io_uring.h

@@ -448,4 +448,15 @@ static inline bool io_file_can_poll(struct io_kiocb *req)
 	}
 	return false;
 }
+
+enum {
+	IO_CHECK_CQ_OVERFLOW_BIT,
+	IO_CHECK_CQ_DROPPED_BIT,
+};
+
+static inline bool io_has_work(struct io_ring_ctx *ctx)
+{
+	return test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq) ||
+	       !llist_empty(&ctx->work_llist);
+}
 #endif

io_uring/napi.c

@@ -122,7 +122,7 @@ static bool io_napi_busy_loop_should_end(void *data,
 
 	if (signal_pending(current))
 		return true;
-	if (io_should_wake(iowq))
+	if (io_should_wake(iowq) || io_has_work(iowq->ctx))
 		return true;
 	if (io_napi_busy_loop_timeout(start_time, iowq->napi_busy_poll_to))
 		return true;