io_uring: add async data clear/free helpers

Futex recently had an issue where it mishandled how ->async_data and
REQ_F_ASYNC_DATA is handled. To avoid future issues like that, add a set
of helpers that either clear or clear-and-free the async data assigned
to a struct io_kiocb.

Convert existing manual handling of that to use the helpers. No intended
functional changes in this patch.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/futex.c

@@ -43,7 +43,6 @@ void io_futex_cache_free(struct io_ring_ctx *ctx)
 
 static void __io_futex_complete(struct io_kiocb *req, io_tw_token_t tw)
 {
-	req->async_data = NULL;
 	hlist_del_init(&req->hash_node);
 	io_req_task_complete(req, tw);
 }
@@ -54,6 +53,7 @@ static void io_futex_complete(struct io_kiocb *req, io_tw_token_t tw)
 
 	io_tw_lock(ctx, tw);
 	io_cache_free(&ctx->futex_cache, req->async_data);
+	io_req_async_data_clear(req, 0);
 	__io_futex_complete(req, tw);
 }
 
@@ -72,8 +72,7 @@ static void io_futexv_complete(struct io_kiocb *req, io_tw_token_t tw)
 			io_req_set_res(req, res, 0);
 	}
 
-	kfree(req->async_data);
-	req->flags &= ~REQ_F_ASYNC_DATA;
+	io_req_async_data_free(req);
 	__io_futex_complete(req, tw);
 }
 
@@ -232,9 +231,7 @@ int io_futexv_wait(struct io_kiocb *req, unsigned int issue_flags)
 		io_ring_submit_unlock(ctx, issue_flags);
 		req_set_fail(req);
 		io_req_set_res(req, ret, 0);
-		kfree(futexv);
-		req->async_data = NULL;
-		req->flags &= ~REQ_F_ASYNC_DATA;
+		io_req_async_data_free(req);
 		return IOU_COMPLETE;
 	}
 
@@ -310,9 +307,7 @@ done:
 	if (ret < 0)
 		req_set_fail(req);
 	io_req_set_res(req, ret, 0);
-	req->async_data = NULL;
-	req->flags &= ~REQ_F_ASYNC_DATA;
-	kfree(ifd);
+	io_req_async_data_free(req);
 	return IOU_COMPLETE;
 }
 

io_uring/io_uring.h

@@ -281,6 +281,19 @@ static inline bool req_has_async_data(struct io_kiocb *req)
 	return req->flags & REQ_F_ASYNC_DATA;
 }
 
+static inline void io_req_async_data_clear(struct io_kiocb *req,
+					   io_req_flags_t extra_flags)
+{
+	req->flags &= ~(REQ_F_ASYNC_DATA|extra_flags);
+	req->async_data = NULL;
+}
+
+static inline void io_req_async_data_free(struct io_kiocb *req)
+{
+	kfree(req->async_data);
+	io_req_async_data_clear(req, 0);
+}
+
 static inline void io_put_file(struct io_kiocb *req)
 {
 	if (!(req->flags & REQ_F_FIXED_FILE) && req->file)

io_uring/net.c

@@ -178,10 +178,8 @@ static void io_netmsg_recycle(struct io_kiocb *req, unsigned int issue_flags)
 	if (hdr->vec.nr > IO_VEC_CACHE_SOFT_CAP)
 		io_vec_free(&hdr->vec);
 
-	if (io_alloc_cache_put(&req->ctx->netmsg_cache, hdr)) {
-		req->async_data = NULL;
-		req->flags &= ~(REQ_F_ASYNC_DATA|REQ_F_NEED_CLEANUP);
-	}
+	if (io_alloc_cache_put(&req->ctx->netmsg_cache, hdr))
+		io_req_async_data_clear(req, REQ_F_NEED_CLEANUP);
 }
 
 static struct io_async_msghdr *io_msg_alloc_async(struct io_kiocb *req)

io_uring/rw.c

@@ -154,10 +154,8 @@ static void io_rw_recycle(struct io_kiocb *req, unsigned int issue_flags)
 	if (rw->vec.nr > IO_VEC_CACHE_SOFT_CAP)
 		io_vec_free(&rw->vec);
 
-	if (io_alloc_cache_put(&req->ctx->rw_cache, rw)) {
-		req->async_data = NULL;
-		req->flags &= ~REQ_F_ASYNC_DATA;
-	}
+	if (io_alloc_cache_put(&req->ctx->rw_cache, rw))
+		io_req_async_data_clear(req, 0);
 }
 
 static void io_req_rw_cleanup(struct io_kiocb *req, unsigned int issue_flags)

io_uring/uring_cmd.c

@@ -37,8 +37,7 @@ static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (io_alloc_cache_put(&req->ctx->cmd_cache, ac)) {
 		ioucmd->sqe = NULL;
-		req->async_data = NULL;
-		req->flags &= ~(REQ_F_ASYNC_DATA|REQ_F_NEED_CLEANUP);
+		io_req_async_data_clear(req, REQ_F_NEED_CLEANUP);
 	}
 }
 

io_uring/waitid.c

@@ -37,9 +37,7 @@ static void io_waitid_free(struct io_kiocb *req)
 	struct io_waitid_async *iwa = req->async_data;
 
 	put_pid(iwa->wo.wo_pid);
-	kfree(req->async_data);
-	req->async_data = NULL;
-	req->flags &= ~REQ_F_ASYNC_DATA;
+	io_req_async_data_free(req);
 }
 
 static bool io_waitid_compat_copy_si(struct io_waitid *iw, int signo)