lkml.org 
[lkml]   [2006]   [May]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH] slab: Fix kmem_cache_destroy() on NUMA
From
Date
With CONFIG_NUMA set, kmem_cache_destroy() may fail and say "Can't
free all objects." The problem is caused by sequences such as the
following (suppose we are on a NUMA machine with two nodes, 0 and 1):

* Allocate an object from cache on node 0.
* Free the object on node 1. The object is put into node 1's alien
array_cache for node 0.
* Call kmem_cache_destroy(), which ultimately ends up in __cache_shrink().
* __cache_shrink() does drain_cpu_caches(), which loops through all nodes.
For each node it drains the shared array_cache and then handles the
alien array_cache for the other node.

However this means that node 0's shared array_cache will be drained,
and then node 1 will move the contents of its alien[0] array_cache
into that same shared array_cache. node 0's shared array_cache is
never looked at again, so the objects left there will appear to be in
use when __cache_shrink() calls __node_shrink() for node 0. So
__node_shrink() will return 1 and kmem_cache_destroy() will fail.

This patch fixes this by having drain_cpu_caches() do
drain_alien_cache() on every node before it does drain_array() on the
nodes' shared array_caches.

The problem was originally reported by Or Gerlitz <ogerlitz@voltaire.com>.

Cc: Christoph Lameter <clameter@sgi.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>

Signed-off-by: Roland Dreier <rolandd@cisco.com>

---

I get a nervous feeling about touching NUMA slab code, because just
the topic alone makes it sound hairy. But I think my diagnosis and
fix are pretty clear, and this definitely fixes crashes seen when
unloading IB modules. It's a regression from 2.6.16, and x86_64
machines with > 1 NUMA node are quite common, so this probably should
go into 2.6.17.

diff --git a/mm/slab.c b/mm/slab.c
index c32af7e..cb747be 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2192,11 +2192,14 @@ static void drain_cpu_caches(struct kmem
check_irq_on();
for_each_online_node(node) {
l3 = cachep->nodelists[node];
- if (l3) {
+ if (l3 && l3->alien)
+ drain_alien_cache(cachep, l3->alien);
+ }
+
+ for_each_online_node(node) {
+ l3 = cachep->nodelists[node];
+ if (l3)
drain_array(cachep, l3, l3->shared, 1, node);
- if (l3->alien)
- drain_alien_cache(cachep, l3->alien);
- }
}
}

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2006-05-15 20:43    [W:0.175 / U:1.692 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site