ext4: protect group inode free counting with group lock

Hello Ted et al,

Commit 6f2e9f0e7d795214b9cf5a47724a273b705fd113 is missing from the 3.4 stable tree. I came across this during testing, and it's pretty easy to trigger under heavy load just by writing out 10,000 8MB files to a disk by way of 8 worker threads. Are there any other significant commits like this that are missing from the 3.4 stable tree? Please note that Tao's original patch doesn't apply entirely cleanly; my tested backport is at the bottom of this email.

-ben
----snip----
[3.4 stable] ext4: protect group inode free counting with group lock

This patch is a straightforward backport of the following commit. During testing I encounted group descriptor corruption that matches Tao's original report. My testing consists of writing 10,000 8MB files to disk using 8 worker threads. This workload manages to trigger the free inode count corruption almost 100% of the time.

commit 6f2e9f0e7d795214b9cf5a47724a273b705fd113
Author: Tao Ma <[email protected]>
Date: Mon May 28 18:20:59 2012 -0400

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.

index c90ab78..30ac458 100644
@@ -782,6 +782,8 @@ 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)) {

@@ -794,8 +796,8 @@ got:
 	}
 	if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
 		gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
-		ext4_unlock_group(sb, group);
 	}
+	ext4_unlock_group(sb, group);
 
 	BUFFER_TRACE(group_desc_bh, "call ext4_handle_dirty_metadata");
 	err = ext4_handle_dirty_metadata(handle, NULL, group_desc_bh);