[PATCH] OOM can panic due to processes stuck in __alloc_pages()

OOM can panic due to the processes stuck in __alloc_pages() doing infinite
rebalance loop while no memory can be reclaimed.  OOM killer tries to kill
some processes, but unfortunetaly, rebalance label was moved by someone
below the TIF_MEMDIE check, so buddy allocator doesn't see that process is
OOM-killed and it can simply fail the allocation :/

Observed in reality on RHEL4(2.6.9)+OpenVZ kernel when a user doing some
memory allocation tricks triggered OOM panic.
Signed-off-by: NDenis Lunev <den@sw.ru>
Signed-off-by: NKirill Korotaev <dev@openvz.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/page_alloc.c

@@ -1180,6 +1180,7 @@ __alloc_pages(gfp_t gfp_mask, unsigned int order,
 
 	/* This allocation should allow future memory freeing. */
 
+rebalance:
 	if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)))
 			&& !in_interrupt()) {
 		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
@@ -1201,7 +1202,6 @@ __alloc_pages(gfp_t gfp_mask, unsigned int order,
 	if (!wait)
 		goto nopage;
 
-rebalance:
 	cond_resched();
 
 	/* We now go into synchronous reclaim */