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>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6768c5aa3feebe58419173bb5c60bab088915328..bd9aff9701c02e43d744a9c1912423b52c21f88b 100644 (file)
--- 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,