linux-kernel - [PATCH] numa: fix slab_node(MPOL

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Date:	Wed, 27 Oct 2010 19:33:43 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Brian Gerst <brgerst@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...e.hu
Subject: [PATCH] numa: fix slab_node(MPOL_BIND)

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@...il.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:


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