ext4: fix deadlock in ext4_remount() and orphan list handling

ext4_orphan_add() and ext4_orphan_del() functions lock sb->s_lock with a
transaction started with ext4_mark_recovery_complete() waits for a transaction
holding sb->s_lock, thus leading to a possible deadlock.  At the moment we
call ext4_mark_recovery_complete() from ext4_remount() we have done all the
work needed for remounting and thus we are safe to drop sb->s_lock before we
wait for transactions to commit.  Note that at this moment we are still
guarded by s_umount lock against other remounts/umounts.

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Eric Sandeen <sandeen@sandeen.net>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6768c5aa3fee..bd9aff9701c0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2222,12 +2222,14 @@ static void ext4_mark_recovery_complete(struct super_block * sb,
 
         jbd2_journal_lock_updates(journal);
         jbd2_journal_flush(journal);
+        lock_super(sb);
         if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER) &&
             sb->s_flags & MS_RDONLY) {
                 EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
                 sb->s_dirt = 0;
                 ext4_commit_super(sb, es, 1);
         }
+        unlock_super(sb);
         jbd2_journal_unlock_updates(journal);
 }
 
@@ -2416,7 +2418,13 @@ static int ext4_remount (struct super_block * sb, int * flags, char * data)
                             (sbi->s_mount_state & EXT4_VALID_FS))
                                 es->s_state = cpu_to_le16(sbi->s_mount_state);
 
+                        /*
+                         * We have to unlock super so that we can wait for
+                         * transactions.
+                         */
+                        unlock_super(sb);
                         ext4_mark_recovery_complete(sb, es);
+                        lock_super(sb);
                 } else {
                         __le32 ret;
                         if ((ret = EXT4_HAS_RO_COMPAT_FEATURE(sb,