From 95599968d19db175829fb580baa6b68939b320fb Mon Sep 17 00:00:00 2001
From: Salman Qazi <sqazi@google.com>
Date: Thu, 31 May 2012 23:52:14 -0400
Subject: [PATCH] ext4: remove mb_groups before tearing down the buddy_cache

We can't have references held on pages in the s_buddy_cache while we are
trying to truncate its pages and put the inode.  All the pages must be
gone before we reach clear_inode.  This can only be gauranteed if we
can prevent new users from grabbing references to s_buddy_cache's pages.

The original bug can be reproduced and the bug fix can be verified by:

while true; do mount -t ext4 /dev/ram0 /export/hda3/ram0; \
	umount /export/hda3/ram0; done &

while true; do cat /proc/fs/ext4/ram0/mb_groups; done

Signed-off-by: Salman Qazi <sqazi@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org
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