From: Valerie Clement Subject: Re: [PATCH] ext4: Fix kernel BUG at fs/ext4/mballoc.c:910! Date: Thu, 14 Feb 2008 13:34:06 +0100 Message-ID: <47B4353E.306@bull.net> References: <1202923172.3508.3.camel@ext1.frec.bull.fr> <20080213203305.GE3029@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-ext4 To: Andreas Dilger Return-path: Received: from ecfrec.frec.bull.fr ([129.183.4.8]:46415 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753676AbYBNMdB (ORCPT ); Thu, 14 Feb 2008 07:33:01 -0500 In-Reply-To: <20080213203305.GE3029@webber.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-ID: Andreas Dilger wrote: > On Feb 13, 2008 18:19 +0100, Valerie Clement wrote: >> From: Valerie Clement >> >> With the flex_bg feature enabled, a large file creation oopses the >> kernel. >> The BUG_ON is: >> BUG_ON(len >= EXT4_BLOCKS_PER_GROUP(sb)); >> >> As the allocation of the bitmaps and the inode table can be done >> outside the block group with flex_bg, this allows to allocate up to >> EXT4_BLOCKS_PER_GROUP blocks in a group. > > Caution is needed here. In the past we were limited to BLOCKS_PER_GROUP() > blocks per extent (32768 blocks at most, regardless of blocksize I think) > but now an extent might be larger. > > Can you please verify that the extent-length limits for "initialized" vs. > "uninitialized" extents are being hit so that extents don't accidentally > grow to be > 32768 blocks long and suddenly get marked as short uninitialized > extents. > > Note that the assertion can still be hit if groups are created with fewer > blocks, or with blocksize < 4096. For example, if we have blocksize = 1024 > this gives BLOCKS_PER_GROUP=8192, but an extent can be up to 32768 blocks. > > I think the right assertion is now: > > BUG_ON(len > EXT4_INIT_MAX_LEN); > > if FLEX_BG is active. I'm not sure if we want to keep the stricter assertion: > > BUG_ON(len > EXT4_HAS_INCOMPAT_FEATURE_FLEX_BG(sb) ? EXT4_INIT_MAX_LEN : > EXT4_BLOCKS_PER_GROUP(sb)); > > but it might be worthwhile at least initially, and I don't think the CPU cost > is very high. I agree. I'll do the changes. > >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c >> index b0f84b4..0275150 100644 >> --- a/fs/ext4/mballoc.c >> +++ b/fs/ext4/mballoc.c >> @@ -907,7 +907,7 @@ static void ext4_mb_mark_free_simple(struct super_block *sb, >> unsigned short chunk; >> unsigned short border; >> >> - BUG_ON(len >= EXT4_BLOCKS_PER_GROUP(sb)); >> + BUG_ON(len > EXT4_BLOCKS_PER_GROUP(sb)); >> >> border = 2 << sb->s_blocksize_bits; >> >> @@ -3286,7 +3286,7 @@ static void ext4_mb_normalize_request(struct ext4_allocation_context *ac, >> } >> BUG_ON(start + size <= ac->ac_o_ex.fe_logical && >> start > ac->ac_o_ex.fe_logical); >> - BUG_ON(size <= 0 || size >= EXT4_BLOCKS_PER_GROUP(ac->ac_sb)); >> + BUG_ON(size <= 0 || size > EXT4_BLOCKS_PER_GROUP(ac->ac_sb)); > > Please separate this into two BUG_ON() statements, so it is clear which > one is being hit. OK. Thanks for review, Valerie