linux-ext4 - Re: [PATCH RESEND] ext4: Fix kernel BUG at fs/ext4/mballoc.c:910!

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Date:	Thu, 14 Feb 2008 15:13:17 -0700
From:	Andreas Dilger <adilger@....com>
To:	Valerie Clement <valerie.clement@...l.net>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Mingming Cao <cmm@...ibm.com>
Subject: Re: [PATCH RESEND] ext4: Fix kernel BUG at fs/ext4/mballoc.c:910!

On Feb 14, 2008  17:35 +0100, Valerie Clement wrote:
> From: Valerie Clement <valerie.clement@...l.net>
> 
> 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.
> Depending on the group size and the block size, extents might be 
> larger than BLOCKS_PER_GROUP(); use EXT_INIT_MAX_LEN instead of 
> BLOCKS_PER_GROUP().

In fact, my earlier review of this patch was incorrect, and Aneesh pointed
out the correct answer.  The ext4_mb_mark_free_simple() function is only
called from ext4_mb_generate_buddy() to generate the buddy bitmap from the
on-disk block bitmap, and in that case the @len parameter should always
be <= EXT4_BLOCKS_PER_GROUP().  I think the original patch was correct.

Sorry about the confusion.  I thought at first glance this was for
freeing the blocks from releasing an extent, but that is incorrect.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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