io_uring: fix overflowed cancel w/ linked ->files

Current io_match_files() check in io_cqring_overflow_flush() is useless
because requests drop ->files before going to the overflow list, however
linked to it request do not, and we don't check them.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1593,14 +1593,29 @@ static void io_cqring_mark_overflow(struct io_ring_ctx *ctx)
 	}
 }
 
-static inline bool io_match_files(struct io_kiocb *req,
-				       struct files_struct *files)
+static inline bool __io_match_files(struct io_kiocb *req,
+				    struct files_struct *files)
 {
+	return ((req->flags & REQ_F_WORK_INITIALIZED) &&
+	        (req->work.flags & IO_WQ_WORK_FILES)) &&
+		req->work.identity->files == files;
+}
+
+static bool io_match_files(struct io_kiocb *req,
+			   struct files_struct *files)
+{
+	struct io_kiocb *link;
+
 	if (!files)
 		return true;
-	if ((req->flags & REQ_F_WORK_INITIALIZED) &&
-	    (req->work.flags & IO_WQ_WORK_FILES))
-		return req->work.identity->files == files;
+	if (__io_match_files(req, files))
+		return true;
+	if (req->flags & REQ_F_LINK_HEAD) {
+		list_for_each_entry(link, &req->link_list, link_list) {
+			if (__io_match_files(link, files))
+				return true;
+		}
+	}
 	return false;
 }
 
@@ -8406,22 +8421,6 @@ static bool io_match_link(struct io_kiocb *preq, struct io_kiocb *req)
 	return false;
 }
 
-static bool io_match_link_files(struct io_kiocb *req,
-				struct files_struct *files)
-{
-	struct io_kiocb *link;
-
-	if (io_match_files(req, files))
-		return true;
-	if (req->flags & REQ_F_LINK_HEAD) {
-		list_for_each_entry(link, &req->link_list, link_list) {
-			if (io_match_files(link, files))
-				return true;
-		}
-	}
-	return false;
-}
-
 /*
  * We're looking to cancel 'req' because it's holding on to our files, but
  * 'req' could be a link to another request. See if it is, and cancel that
@@ -8504,7 +8503,7 @@ static void io_cancel_defer_files(struct io_ring_ctx *ctx,
 
 	spin_lock_irq(&ctx->completion_lock);
 	list_for_each_entry_reverse(de, &ctx->defer_list, list) {
-		if (io_match_link_files(de->req, files)) {
+		if (io_match_files(de->req, files)) {
 			list_cut_position(&list, &ctx->defer_list, &de->list);
 			break;
 		}