ext4: Use new buffer_head flag to check uninit group bitmaps initialization

For uninit block group, the on-disk bitmap is not initialized. That
implies we cannot depend on the uptodate flag on the bitmap
buffer_head to find bitmap validity.  Use a new buffer_head flag which
would be set after we properly initialize the bitmap.  This also
prevents (re-)initializing the uninit group bitmap every time we call 
ext4_read_block_bitmap().

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

1 files changed, 23 insertions, 2 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 1b26b68aa428..6bba06b09dd1 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -320,20 +320,41 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
                             block_group, bitmap_blk);
                 return NULL;
         }
-        if (buffer_uptodate(bh) &&
-            !(desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))
+
+        if (bitmap_uptodate(bh))
                 return bh;
 
         lock_buffer(bh);
+        if (bitmap_uptodate(bh)) {
+                unlock_buffer(bh);
+                return bh;
+        }
         spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group));
         if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
                 ext4_init_block_bitmap(sb, bh, block_group, desc);
+                set_bitmap_uptodate(bh);
                 set_buffer_uptodate(bh);
                 spin_unlock(sb_bgl_lock(EXT4_SB(sb), block_group));
                 unlock_buffer(bh);
                 return bh;
         }
         spin_unlock(sb_bgl_lock(EXT4_SB(sb), block_group));
+        if (buffer_uptodate(bh)) {
+                /*
+                 * if not uninit if bh is uptodate,
+                 * bitmap is also uptodate
+                 */
+                set_bitmap_uptodate(bh);
+                unlock_buffer(bh);
+                return bh;
+        }
+        /*
+         * submit the buffer_head for read. We can
+         * safely mark the bitmap as uptodate now.
+         * We do it here so the bitmap uptodate bit
+         * get set with buffer lock held.
+         */
+        set_bitmap_uptodate(bh);
         if (bh_submit_read(bh) < 0) {
                 put_bh(bh);
                 ext4_error(sb, __func__,