ext4: don't return to userspace after freezing the fs with a mutex held

ext4_freeze() used jbd2_journal_lock_updates() which takes
the j_barrier mutex, and then returns to userspace.  The
kernel does not like this:

================================================
[ BUG: lock held when returning to user space! ]
------------------------------------------------
lvcreate/1075 is leaving the kernel with locks still held!
1 lock held by lvcreate/1075:
 #0:  (&journal->j_barrier){+.+...}, at: [<ffffffff811c6214>]
jbd2_journal_lock_updates+0xe1/0xf0

Use vfs_check_frozen() added to ext4_journal_start_sb() and
ext4_force_commit() instead.

Addresses-Red-Hat-Bugzilla: #568503

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 10 insertions, 10 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e14d22c170d5..00d09f58f188 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -241,6 +241,7 @@ handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
         if (sb->s_flags & MS_RDONLY)
                 return ERR_PTR(-EROFS);
 
+        vfs_check_frozen(sb, SB_FREEZE_WRITE);
         /* Special case here: if the journal has aborted behind our
          * backs (eg. EIO in the commit thread), then we still need to
          * take the FS itself readonly cleanly. */
@@ -3485,8 +3486,10 @@ int ext4_force_commit(struct super_block *sb)
                 return 0;
 
         journal = EXT4_SB(sb)->s_journal;
-        if (journal)
+        if (journal) {
+                vfs_check_frozen(sb, SB_FREEZE_WRITE);
                 ret = ext4_journal_force_commit(journal);
+        }
 
         return ret;
 }
@@ -3535,18 +3538,16 @@ static int ext4_freeze(struct super_block *sb)
          * the journal.
          */
         error = jbd2_journal_flush(journal);
-        if (error < 0) {
-        out:
-                jbd2_journal_unlock_updates(journal);
-                return error;
-        }
+        if (error < 0)
+                goto out;
 
         /* Journal blocked and flushed, clear needs_recovery flag. */
         EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
         error = ext4_commit_super(sb, 1);
-        if (error)
-                goto out;
-        return 0;
+out:
+        /* we rely on s_frozen to stop further updates */
+        jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
+        return error;
 }
 
 /*
@@ -3563,7 +3564,6 @@ static int ext4_unfreeze(struct super_block *sb)
         EXT4_SET_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
         ext4_commit_super(sb, 1);
         unlock_super(sb);
-        jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
         return 0;
 }