ext4: protect group inode free counting with group lock

Now when we set the group inode free count, we don't have a proper
group lock so that multiple threads may decrease the inode free
count at the same time. And e2fsck will complain something like:

Free inodes count wrong for group #1 (1, counted=0).
Fix? no

Free inodes count wrong for group #2 (3, counted=0).
Fix? no

Directories count wrong for group #2 (780, counted=779).
Fix? no

Free inodes count wrong for group #3 (2272, counted=2273).
Fix? no

So this patch try to protect it with the ext4_lock_group.

btw, it is found by xfstests test case 269 and the volume is
mkfsed with the parameter
"-O ^resize_inode,^uninit_bg,extent,meta_bg,flex_bg,ext_attr"
and I have run it 100 times and the error in e2fsck doesn't
show up again.

Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index ea32d7e..03583ab 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -797,7 +797,10 @@ got:
                        ext4_itable_unused_set(sb, gdp,
                                        (EXT4_INODES_PER_GROUP(sb) - ino));
                up_read(&grp->alloc_sem);
+       } else {
+               ext4_lock_group(sb, group);
        }
+
        ext4_free_inodes_set(sb, gdp, ext4_free_inodes_count(sb, gdp) - 1);
        if (S_ISDIR(mode)) {
                ext4_used_dirs_set(sb, gdp, ext4_used_dirs_count(sb, gdp) + 1);
@@ -811,8 +814,8 @@ got:
                ext4_inode_bitmap_csum_set(sb, group, gdp, inode_bitmap_bh,
                                           EXT4_INODES_PER_GROUP(sb) / 8);
                ext4_group_desc_csum_set(sb, group, gdp);
-               ext4_unlock_group(sb, group);
        }
+       ext4_unlock_group(sb, group);
 
        BUFFER_TRACE(inode_bitmap_bh, "call ext4_handle_dirty_metadata");
        err = ext4_handle_dirty_metadata(handle, NULL, inode_bitmap_bh);