xfs: initialise attrd item to zero

On the first allocation of a attrd item, xfs_trans_add_item() fires
an assert like so:

 XFS (pmem0): EXPERIMENTAL logged extended attributes feature added. Use at your own risk!
 XFS: Assertion failed: !test_bit(XFS_LI_DIRTY, &lip->li_flags), file: fs/xfs/xfs_trans.c, line: 683
 ------------[ cut here ]------------
 kernel BUG at fs/xfs/xfs_message.c:102!
 Call Trace:
  <TASK>
  xfs_trans_add_item+0x17e/0x190
  xfs_trans_get_attrd+0x67/0x90
  xfs_attr_create_done+0x13/0x20
  xfs_defer_finish_noroll+0x100/0x690
  __xfs_trans_commit+0x144/0x330
  xfs_trans_commit+0x10/0x20
  xfs_attr_set+0x3e2/0x4c0
  xfs_initxattrs+0xaa/0xe0
  security_inode_init_security+0xb0/0x130
  xfs_init_security+0x18/0x20
  xfs_generic_create+0x13a/0x340
  xfs_vn_create+0x17/0x20
  path_openat+0xff3/0x12f0
  do_filp_open+0xb2/0x150

The attrd log item is allocated via kmem_cache_alloc, and
xfs_log_item_init() does not zero the entire log item structure - it
assumes that the structure is already all zeros as it only
initialises non-zero fields. Fix the attr items to be allocated
via the *zalloc methods.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Allison Henderson<allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_attr_item.c

@@ -728,7 +728,7 @@ xfs_trans_get_attrd(struct xfs_trans		*tp,
 
 	ASSERT(tp != NULL);
 
-	attrdp = kmem_cache_alloc(xfs_attrd_cache, GFP_NOFS | __GFP_NOFAIL);
+	attrdp = kmem_cache_zalloc(xfs_attrd_cache, GFP_NOFS | __GFP_NOFAIL);
 
 	xfs_log_item_init(tp->t_mountp, &attrdp->attrd_item, XFS_LI_ATTRD,
 			  &xfs_attrd_item_ops);