[PATCH] ext4: Protect group inode free counting with group lock.

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From: Tao Ma <boyu.mt@xxxxxxxxxx>

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 I have run it 100
times and the error in e2fsck doesn't show up again.

Cc: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Tao Ma <boyu.mt@xxxxxxxxxx>
 fs/ext4/ialloc.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 409c2ee..25595e2 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -772,7 +772,9 @@ got:
 			ext4_itable_unused_set(sb, gdp,
 					(EXT4_INODES_PER_GROUP(sb) - ino));
-	}
+	} 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);
@@ -782,10 +784,9 @@ got:
 		gdp->bg_checksum = ext4_group_desc_csum(sbi, 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);

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