[PATCH] numa: fix slab_node(MPOL_BIND)

From: Eric Dumazet <eric.dumazet@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Brian Gerst <brgerst@gmail.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, mingo@elte.hu
Subject: [PATCH] numa: fix slab_node(MPOL_BIND)
Date: Wed, 27 Oct 2010 19:33:43 +0200	[thread overview]
Message-ID: <1288200823.5619.46.camel@edumazet-laptop> (raw)
In-Reply-To: <1288195668.2709.167.camel@edumazet-laptop>

Le mercredi 27 octobre 2010 à 18:07 +0200, Eric Dumazet a écrit :

> So I tried following experiment :
> 
> # swapoff
> # numactl --membind=0 swapon -a
> # grep swap /proc/vmallocinfo 
> 0xf9bf3000-0xf9cf4000 1052672 sys_swapon+0x4aa/0xb24 pages=256 vmalloc N0=256
> # swapoff -a
> # numactl --membind=1 swapon -a
> 
> <<FREEZE>>
> 

Crash in fact, not freeze, in slab_node()

Problem is : we dereference a NULL zone pointer.

(node 1 has HighMem only)

Following patch seems to solve the problem for me

# swapoff -a
# numactl --membind=1 swapon -a
# grep swap /proc/vmallocinfo 
0xf9da5000-0xf9ea6000 1052672 sys_swapon+0x3f9/0xa34 pages=256 vmalloc N1=256


Thanks


[PATCH] numa: fix slab_node(MPOL_BIND) 

When a node contains only HighMem memory, slab_node(MPOL_BIND)
dereferences a NULL pointer.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 mm/mempolicy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 81a1276..4a57f13 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1597,7 +1597,7 @@ unsigned slab_node(struct mempolicy *policy)
 		(void)first_zones_zonelist(zonelist, highest_zoneidx,
 							&policy->v.nodes,
 							&zone);
-		return zone->node;
+		return zone ? zone->node : numa_node_id();
 	}
 
 	default:


