linux-ext4 - [PATCH 2/2] ext4: remove mb_groups before tearing buddy

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Message-ID: <20120529233614.12259.28652.stgit@dungbeetle.mtv.corp.google.com>
Date:	Tue, 29 May 2012 16:36:14 -0700
From:	Salman Qazi <sqazi@...gle.com>
To:	Ted Ts'o <tytso@...gle.com>, linux-ext4@...r.kernel.org
Subject: [PATCH 2/2] ext4: remove mb_groups before tearing 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@...gle.com>
---
 fs/ext4/mballoc.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5c315ab..6b0a57e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2517,6 +2517,9 @@ int ext4_mb_release(struct super_block *sb)
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);
 
+	if (sbi->s_proc)
+		remove_proc_entry("mb_groups", sbi->s_proc);
+
 	if (sbi->s_group_info) {
 		for (i = 0; i < ngroups; i++) {
 			grinfo = ext4_get_group_info(sb, i);
@@ -2564,8 +2567,6 @@ int ext4_mb_release(struct super_block *sb)
 	}
 
 	free_percpu(sbi->s_locality_groups);
-	if (sbi->s_proc)
-		remove_proc_entry("mb_groups", sbi->s_proc);
 
 	return 0;
 }

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