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ext4: Clarify the locking details in mballoc

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We don't need to take the alloc_sem lock when we are adding new
groups, since mballoc won't see the new group added until we bump
sbi->s_groups_count.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
This commit is contained in:
Aneesh Kumar K.V
2009-09-09 23:50:17 -04:00
committed by Theodore Ts'o
parent f41c075053
commit 08c3a81338
2 changed files with 6 additions and 8 deletions
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7
fs/ext4/mballoc.c
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@@ -928,8 +928,11 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
this_grp = ext4_get_group_info(sb, group);
/*
* This ensures we don't add group
* to this buddy cache via resize
* This ensures that we don't reinit the buddy cache
* page which map to the group from which we are already
* allocating. If we are looking at the buddy cache we would
* have taken a reference using ext4_mb_load_buddy and that
* would have taken the alloc_sem lock.
*/
num_grp_locked = ext4_mb_get_buddy_cache_lock(sb, group);
if (!EXT4_MB_GRP_NEED_INIT(this_grp)) {