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

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

[Kirill Korotaev]

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: Denis Lunev <den@sw.ru>
Signed-Off-By: Kirill Korotaev <dev@openvz.org>

--- ./mm/page_alloc.c.oomx	2006-11-08 17:44:16.000000000 +0300
+++ ./mm/page_alloc.c	2006-11-13 21:57:33.000000000 +0300
@@ -1251,6 +1251,7 @@ restart:
 
 	/* 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)) {
@@ -1272,7 +1273,6 @@ nofail_alloc:
 	if (!wait)
 		goto nopage;
 
-rebalance:
 	cond_resched();
 
 	/* We now go into synchronous reclaim */

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

[Andrew Morton]

On Mon, 13 Nov 2006 22:13:47 +0300
Kirill Korotaev <dev@openvz.org> wrote:

> 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: Denis Lunev <den@sw.ru>
> Signed-Off-By: Kirill Korotaev <dev@openvz.org>
> 
> --- ./mm/page_alloc.c.oomx	2006-11-08 17:44:16.000000000 +0300
> +++ ./mm/page_alloc.c	2006-11-13 21:57:33.000000000 +0300
> @@ -1251,6 +1251,7 @@ restart:
>  
>  	/* 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)) {
> @@ -1272,7 +1273,6 @@ nofail_alloc:
>  	if (!wait)
>  		goto nopage;
>  
> -rebalance:
>  	cond_resched();
>  
>  	/* We now go into synchronous reclaim */

Your patch reverts a change made by Nick's
a457c255ae59b5f7f52f63fc88d5e530101772c6 two years ago.

It looks right to me, but the original change was unchangelogged and I
wonder what it was aiming to do?