From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752049AbcEPL7O (ORCPT ); Mon, 16 May 2016 07:59:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:47353 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750785AbcEPL7N (ORCPT ); Mon, 16 May 2016 07:59:13 -0400 Subject: Re: [PATCH] tmpfs: don't undo fallocate past its last page To: Anthony Romano , hughd@google.com References: <1462713387-16724-1-git-send-email-anthony.romano@coreos.com> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Vlastimil Babka Message-ID: <5739B60E.1090700@suse.cz> Date: Mon, 16 May 2016 13:59:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <1462713387-16724-1-git-send-email-anthony.romano@coreos.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/08/2016 03:16 PM, Anthony Romano wrote: > When fallocate is interrupted it will undo a range that extends one byte > past its range of allocated pages. This can corrupt an in-use page by > zeroing out its first byte. Instead, undo using the inclusive byte range. Huh, good catch. So why is shmem_undo_range() adding +1 to the value in the first place? The only other caller is shmem_truncate_range() and all *its* callers do subtract 1 to avoid the same issue. So a nicer fix would be to remove all this +1/-1 madness. Or is there some subtle corner case I'm missing? > Signed-off-by: Anthony Romano Looks like a stable candidate patch. Can you point out the commit that introduced the bug, for the Fixes: tag? Thanks, Vlastimil > --- > mm/shmem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 719bd6b..f0f9405 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2238,7 +2238,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, > /* Remove the !PageUptodate pages we added */ > shmem_undo_range(inode, > (loff_t)start << PAGE_SHIFT, > - (loff_t)index << PAGE_SHIFT, true); > + ((loff_t)index << PAGE_SHIFT) - 1, true); > goto undone; > } > >