ext4: check for need init flag in ext4_mb_load_buddy

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>

1 files changed, 18 insertions, 21 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index fed5ac699141..484c9d10c7fa 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1034,8 +1034,26 @@ 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.
@@ -2012,27 +2030,6 @@ 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;