From: =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= Subject: Re: [PATCH] ext4: fix wrong size computation in ext4_mb_normalize_request() Date: Thu, 10 Jul 2014 11:25:07 +0200 (CEST) Message-ID: References: <1404970836-21357-1-git-send-email-wangxg.fnst@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, mlombard@redhat.com To: Xiaoguang Wang Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59358 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752135AbaGJJZQ (ORCPT ); Thu, 10 Jul 2014 05:25:16 -0400 In-Reply-To: <1404970836-21357-1-git-send-email-wangxg.fnst@cn.fujitsu.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, 10 Jul 2014, Xiaoguang Wang wrote: > Date: Thu, 10 Jul 2014 13:40:36 +0800 > From: Xiaoguang Wang > To: linux-ext4@vger.kernel.org > Cc: tytso@mit.edu, mlombard@redhat.com, > Xiaoguang Wang > Subject: [PATCH] ext4: fix wrong size computation in > ext4_mb_normalize_request() > > As the member fe_len defined in struct ext4_free_extent is expressed as > number of clusters, the variable "size" computation is wrong, we need to > first translate it to block number, then to bytes. > > Signed-off-by: Xiaoguang Wang > --- > fs/ext4/mballoc.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 7f72f50..9a543b5 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -3076,7 +3076,8 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac, > size = 8 * 1024 * 1024; > } else { > start_off = (loff_t)ac->ac_o_ex.fe_logical << bsbits; > - size = ac->ac_o_ex.fe_len << bsbits; > + size = EXT4_C2B(EXT4_SB(ac->ac_sb), > + ac->ac_o_ex.fe_len) << bsbits; There is a patch out there up for more discussion which rewrites a whole bunch of code in ext4_mb_normalize_request(). But more importantly this fix, while correct is not going to change anything since this condition will never be run. Btw, I take back the correct part since it seems that there is a a possibility of overflow. This should be better. size = (loff_t)EXT4_C2B(EXT4_SB(ac->ac_sb), ac->ac_o_ex.fe_len) << bsbits; Thanks! -Lukas > } > size = size >> bsbits; > start = start_off >> bsbits; >