io_uring: complete notifiers in tw

We need a task context to post CQEs but using wq is too expensive.
Try to complete notifiers using task_work and fall back to wq if fails.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/089799ab665b10b78fdc614ae6d59fa7ef0d5f91.1657643355.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 19 insertions, 3 deletions

diff --git a/io_uring/notif.c b/io_uring/notif.c
index b257db2120b4..aec74f88fc33 100644
--- a/io_uring/notif.c
+++ b/io_uring/notif.c
@@ -13,6 +13,11 @@ static void __io_notif_complete_tw(struct callback_head *cb)
 	struct io_notif *notif = container_of(cb, struct io_notif, task_work);
 	struct io_ring_ctx *ctx = notif->ctx;
 
+	if (likely(notif->task)) {
+		io_put_task(notif->task, 1);
+		notif->task = NULL;
+	}
+
 	io_cq_lock(ctx);
 	io_fill_cqe_aux(ctx, notif->tag, 0, notif->seq, true);
 
@@ -43,6 +48,14 @@ static void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
 
 	if (!refcount_dec_and_test(&uarg->refcnt))
 		return;
+
+	if (likely(notif->task)) {
+		init_task_work(&notif->task_work, __io_notif_complete_tw);
+		if (likely(!task_work_add(notif->task, &notif->task_work,
+					  TWA_SIGNAL)))
+			return;
+	}
+
 	INIT_WORK(&notif->commit_work, io_notif_complete_wq);
 	queue_work(system_unbound_wq, &notif->commit_work);
 }
@@ -134,12 +147,15 @@ __cold int io_notif_unregister(struct io_ring_ctx *ctx)
 	for (i = 0; i < ctx->nr_notif_slots; i++) {
 		struct io_notif_slot *slot = &ctx->notif_slots[i];
 
-		if (slot->notif)
-			io_notif_slot_flush(slot);
+		if (!slot->notif)
+			continue;
+		if (WARN_ON_ONCE(slot->notif->task))
+			slot->notif->task = NULL;
+		io_notif_slot_flush(slot);
 	}
 
 	kvfree(ctx->notif_slots);
 	ctx->notif_slots = NULL;
 	ctx->nr_notif_slots = 0;
 	return 0;
-}
\ No newline at end of file
+}