ext4: Clarify the locking details in mballoc
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>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 484c9d1..d23056d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -928,8 +928,11 @@
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)) {
