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>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index fed5ac6..484c9d1 100644 (file)
--- 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;