From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757406AbcGJXqq (ORCPT ); Sun, 10 Jul 2016 19:46:46 -0400 Received: from mail-oi0-f43.google.com ([209.85.218.43]:36728 "EHLO mail-oi0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757269AbcGJXqm (ORCPT ); Sun, 10 Jul 2016 19:46:42 -0400 Date: Sun, 10 Jul 2016 16:46:32 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Linus Torvalds cc: Anthony Romano , Brandon Philips , Andrew Morton , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] tmpfs: fix regression hang in fallocate undo Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The well-spotted fallocate undo fix is good in most cases, but not when fallocate failed on the very first page. index 0 then passes lend -1 to shmem_undo_range(), and that has two bad effects: (a) that it will undo every fallocation throughout the file, unrestricted by the current range; but more importantly (b) it can cause the undo to hang, because lend -1 is treated as truncation, which makes it keep on retrying until every page has gone, but those already fully instantiated will never go away. Big thank you to xfstests generic/269 which demonstrates this. Fixes: b9b4bb26af01 ("tmpfs: don't undo fallocate past its last page") Cc: stable@vger.kernel.org Signed-off-by: Hugh Dickins --- mm/shmem.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- 4.7-rc6/mm/shmem.c 2016-06-26 22:02:27.543373427 -0700 +++ linux/mm/shmem.c 2016-07-10 15:19:24.000000000 -0700 @@ -2225,9 +2225,11 @@ static long shmem_fallocate(struct file error = shmem_getpage(inode, index, &page, SGP_FALLOC); if (error) { /* Remove the !PageUptodate pages we added */ - shmem_undo_range(inode, - (loff_t)start << PAGE_SHIFT, - ((loff_t)index << PAGE_SHIFT) - 1, true); + if (index > start) { + shmem_undo_range(inode, + (loff_t)start << PAGE_SHIFT, + ((loff_t)index << PAGE_SHIFT) - 1, true); + } goto undone; }