[PATCH] Ext4: wait for log to commit when putting super

[Josef Bacik <josef@redhat.com>]

There is a problem where a transaction will be committing while we're unmounting
the filesystem and you will get a panic because EXT4_SB(sb)->s_group_info has
been kfree'ed in ext4_put_super.  The commit code does the callback for the
mballoc stuff to release free'ed blocks in the transaction and panic's trying to
access s_group_info.  The fix is to wait for the transaction to finish
committing before we start cleaning up the mballoc stuff.  This patch hasn't
been tested yet, but its an obvious fix.

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/ext4/super.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d4ca92a..ddd115f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -593,6 +593,7 @@ static void ext4_put_super(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_super_block *es = sbi->s_es;
+	tid_t target;
 	int i, err;
 
 	flush_workqueue(sbi->dio_unwritten_wq);
@@ -603,6 +604,9 @@ static void ext4_put_super(struct super_block *sb)
 	if (sb->s_dirt)
 		ext4_commit_super(sb, 1);
 
+	if (jbd2_journal_start_commit(EXT4_SB(sb)->s_journal, &target))
+		jbd2_log_wait_commit(EXT4_SB(sb)->s_journal, target);
+
 	ext4_release_system_zone(sb);
 	ext4_mb_release(sb);
 	ext4_ext_release(sb);
-- 
1.6.2.5