We should check for need init flag with group info alloc_sem
held. That would make sure when 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 for the need init flag check in
ext4_mb_regular_allocator because doing the check without holding
alloc_sem is racy
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
---
fs/ext4/mballoc.c | 39 ++++++++++++++++++---------------------
1 files changed, 18 insertions(+), 21 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 78e907d..4ed869e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1032,8 +1032,26 @@ ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
* 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.
@@ -2015,27 +2033,6 @@ 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;
--
1.6.4.2.253.g0b1fac
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