From: Badari Pulavarty <pbadari@us.ibm.com>

Alexey Dobriyan reported ext2 discard reservation panic while ago
(http://lkml.org/lkml/2007/3/2/138).  If ext2_new_inode() fails for any
reason it would end up calling ext2_discard_reservation() (due to last
iput).  Normally, it does nothing since we don't have a reservation window
structure allocated.  But the NULL pointer check wouldn't work with slab
poisioning, and causes oops.

Fix is to initialize i_block_alloc_info to NULL in ext2_alloc_inode()
code instead of assuming that it would be NULL. Same fix already
exists in ext3 and ext4.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Cc: "Martin J. Bligh" <mbligh@mbligh.org>
Cc: Valerie Henson <val@nmt.edu>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/ext2/super.c |    1 +
 1 file changed, 1 insertion(+)

diff -puN fs/ext2/super.c~fix-for-ext2-reservation fs/ext2/super.c
--- a/fs/ext2/super.c~fix-for-ext2-reservation
+++ a/fs/ext2/super.c
@@ -149,6 +149,7 @@ static struct inode *ext2_alloc_inode(st
 	ei->i_acl = EXT2_ACL_NOT_CACHED;
 	ei->i_default_acl = EXT2_ACL_NOT_CACHED;
 #endif
+	ei->i_block_alloc_info = NULL;
 	ei->vfs_inode.i_version = 1;
 	return &ei->vfs_inode;
 }
_