linux-kernel - [ 100/123] fs: Fix imbalance in freeze protection in mark_files

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Date:	Wed,  9 Jan 2013 12:35:39 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Zdenek Kabelac <zkabelac@...hat.com>,
	Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>
Subject: [ 100/123] fs: Fix imbalance in freeze protection in mark_files_ro()

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit 72651cac884b1e285fa8e8314b10e9f1b8458802 upstream.

File descriptors (even those for writing) do not hold freeze protection.
Thus mark_files_ro() must call __mnt_drop_write() to only drop protection
against remount read-only. Calling mnt_drop_write_file() as we do now
results in:

[ BUG: bad unlock balance detected! ]
3.7.0-rc6-00028-g88e75b6 #101 Not tainted
-------------------------------------
kworker/1:2/79 is trying to release lock (sb_writers) at:
[<ffffffff811b33b4>] mnt_drop_write+0x24/0x30
but there are no more locks to release!

Reported-by: Zdenek Kabelac <zkabelac@...hat.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/file_table.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -458,8 +458,8 @@ void mark_files_ro(struct super_block *s
 		spin_unlock(&f->f_lock);
 		if (file_check_writeable(f) != 0)
 			continue;
+		__mnt_drop_write(f->f_path.mnt);
 		file_release_write(f);
-		mnt_drop_write_file(f);
 	} while_file_list_for_each_entry;
 	lg_global_unlock(&files_lglock);
 }


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