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Subject[26/90] ext4: check for need init flag in ext4_mb_load_buddy
2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
(cherry picked from commit f41c0750538667b87a19c93952e5d42fcc069bd7)

We should check for need init flag with the group's alloc_sem held, to
make sure while we are loading the buddy cache and holding a reference
to it, a file system resize can't add new blocks to same group.

The patch also drops the need init flag check in
ext4_mb_regular_allocator() because doing the check without holding
alloc_sem is racy.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/mballoc.c | 39 ++++++++++++++++++---------------------
1 file changed, 18 insertions(+), 21 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1032,8 +1032,26 @@ ext4_mb_load_buddy(struct super_block *s
* groups mapped by the page is blocked
* till we are done with allocation
*/
+repeat_load_buddy:
down_read(e4b->alloc_semp);

+ if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
+ /* we need to check for group need init flag
+ * with alloc_semp held so that we can be sure
+ * that new blocks didn't get added to the group
+ * when we are loading the buddy cache
+ */
+ up_read(e4b->alloc_semp);
+ /*
+ * we need full data about the group
+ * to make a good selection
+ */
+ ret = ext4_mb_init_group(sb, group);
+ if (ret)
+ return ret;
+ goto repeat_load_buddy;
+ }
+
/*
* the buddy cache inode stores the block bitmap
* and buddy information in consecutive blocks.
@@ -2010,27 +2028,6 @@ repeat:
if (grp->bb_free == 0)
continue;

- /*
- * if the group is already init we check whether it is
- * a good group and if not we don't load the buddy
- */
- if (EXT4_MB_GRP_NEED_INIT(grp)) {
- /*
- * we need full data about the group
- * to make a good selection
- */
- err = ext4_mb_init_group(sb, group);
- if (err)
- goto out;
- }
-
- /*
- * If the particular group doesn't satisfy our
- * criteria we continue with the next group
- */
- if (!ext4_mb_good_group(ac, group, cr))
- continue;
-
err = ext4_mb_load_buddy(sb, group, &e4b);
if (err)
goto out;



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