From: Robin Dong <sanbai@taobao.com>
Date: Wed, 26 Oct 2011 09:14:27 +0000 (-0400)
Subject: ext4: use stream-alloc when mb_group_prealloc set to zero
X-Git-Tag: v3.2-rc1~85^2~29
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ebbe027797f67d34708ccfabdb129886d549f9ce;p=pandora-kernel.git

ext4: use stream-alloc when mb_group_prealloc set to zero

The kernel will crash on

ext4_mb_mark_diskspace_used:
	BUG_ON(ac->ac_b_ex.fe_len <= 0);

after we set /sys/fs/ext4/sda/mb_group_prealloc to zero and create new files in an ext4 filesystem.

The reason is: ac_b_ex.fe_len also set to zero(mb_group_prealloc) in ext4_mb_normalize_group_request
because the ac_flags contains EXT4_MB_HINT_GROUP_ALLOC.

I think when someone set mb_group_prealloc to zero, it means DO NOT USE GROUP PREALLOCATION,
so we should set alloc-strategy to STREAM in this case.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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