mm/memcontrol.c: fix uninitialized variable use in mem_cgroup_move_parent()

In mm/memcontrol.c::mem_cgroup_move_parent() there's a path that jumps
to the 'put_back' label

  	ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge);
  	if (ret || !parent)
  		goto put_back;

where we'll

  	if (charge > PAGE_SIZE)
  		compound_unlock_irqrestore(page, flags);

but, we have not assigned anything to 'flags' at this point, nor have we
called 'compound_lock_irqsave()' (which is what sets 'flags').  The
'put_back' label should be moved below the call to
compound_unlock_irqrestore() as per this patch.
Signed-off-by: NJesper Juhl <jj@chaosbits.net>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2292,9 +2292,10 @@ static int mem_cgroup_move_parent(struct page_cgroup *pc,
 	ret = mem_cgroup_move_account(pc, child, parent, true, charge);
 	if (ret)
 		mem_cgroup_cancel_charge(parent, charge);
-put_back:
+
 	if (charge > PAGE_SIZE)
 		compound_unlock_irqrestore(page, flags);
+put_back:
 	putback_lru_page(page);
 put:
 	put_page(page);