io_uring: pass struct io_tw_state by value

8e5b3b8 ("io_uring: remove struct io_tw_state::locked") removed the
only field of io_tw_state but kept it as a task work callback argument
to "forc[e] users not to invoke them carelessly out of a wrong context".
Passing the struct io_tw_state * argument adds a few instructions to all
callers that can't inline the functions and see the argument is unused.

So pass struct io_tw_state by value instead. Since it's a 0-sized value,
it can be passed without any instructions needed to initialize it.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250217022511.1150145-2-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -444,7 +444,7 @@ struct io_ring_ctx {
 struct io_tw_state {
 };
 /* Alias to use in code that doesn't instantiate struct io_tw_state */
-typedef struct io_tw_state *io_tw_token_t;
+typedef struct io_tw_state io_tw_token_t;
 
 enum {
 	REQ_F_FIXED_FILE_BIT	= IOSQE_FIXED_FILE_BIT,

io_uring/io_uring.c

@@ -255,7 +255,7 @@ static __cold void io_fallback_req_func(struct work_struct *work)
 	percpu_ref_get(&ctx->refs);
 	mutex_lock(&ctx->uring_lock);
 	llist_for_each_entry_safe(req, tmp, node, io_task_work.node)
-		req->io_task_work.func(req, &ts);
+		req->io_task_work.func(req, ts);
 	io_submit_flush_completions(ctx);
 	mutex_unlock(&ctx->uring_lock);
 	percpu_ref_put(&ctx->refs);
@@ -1052,24 +1052,24 @@ struct llist_node *io_handle_tw_list(struct llist_node *node,
 						    io_task_work.node);
 
 		if (req->ctx != ctx) {
-			ctx_flush_and_put(ctx, &ts);
+			ctx_flush_and_put(ctx, ts);
 			ctx = req->ctx;
 			mutex_lock(&ctx->uring_lock);
 			percpu_ref_get(&ctx->refs);
 		}
 		INDIRECT_CALL_2(req->io_task_work.func,
 				io_poll_task_func, io_req_rw_complete,
-				req, &ts);
+				req, ts);
 		node = next;
 		(*count)++;
 		if (unlikely(need_resched())) {
-			ctx_flush_and_put(ctx, &ts);
+			ctx_flush_and_put(ctx, ts);
 			ctx = NULL;
 			cond_resched();
 		}
 	} while (node && *count < max_entries);
 
-	ctx_flush_and_put(ctx, &ts);
+	ctx_flush_and_put(ctx, ts);
 	return node;
 }
 
@@ -1341,7 +1341,7 @@ static inline int io_run_local_work_locked(struct io_ring_ctx *ctx,
 
 	if (!io_local_work_pending(ctx))
 		return 0;
-	return __io_run_local_work(ctx, &ts, min_events,
+	return __io_run_local_work(ctx, ts, min_events,
 					max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
 }
 
@@ -1352,7 +1352,7 @@ static int io_run_local_work(struct io_ring_ctx *ctx, int min_events,
 	int ret;
 
 	mutex_lock(&ctx->uring_lock);
-	ret = __io_run_local_work(ctx, &ts, min_events, max_events);
+	ret = __io_run_local_work(ctx, ts, min_events, max_events);
 	mutex_unlock(&ctx->uring_lock);
 	return ret;
 }