2006-02-09 18:29:18

by Ravikiran G Thirumalai

Subject: [patch] slab: Avoid deadlock at kmem_cache_create/kmem_cache_destroy

Prevents deadlock situation between kmem_cache_create()/kmem_cache_destory(),
and kmem_cache_create() /cpu hotplug. The locking order probably got
moved over time.

Signed-off-by: Ravikiran Thirumalai <[email protected]>
Signed-off-by: Shai Fultheim <[email protected]>

Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c 2006-02-08 13:13:23.000000000 -0800
+++ linux-2.6/mm/slab.c 2006-02-09 01:58:02.000000000 -0800
@@ -1718,6 +1718,13 @@ kmem_cache_create (const char *name, siz
BUG();
}

+ /*
+ * Don't let CPUs to come and go.
+ * Note: preserve lock taking order -- lock_cpu_hotplug first,
+ * cache_chain_mutex then.
+ */
+ lock_cpu_hotplug();
+
mutex_lock(&cache_chain_mutex);

list_for_each(p, &cache_chain) {
@@ -1918,8 +1925,6 @@ kmem_cache_create (const char *name, siz
cachep->dtor = dtor;
cachep->name = name;

- /* Don't let CPUs to come and go */
- lock_cpu_hotplug();

if (g_cpucache_up == FULL) {
enable_cpucache(cachep);
@@ -1978,12 +1983,12 @@ kmem_cache_create (const char *name, siz

/* cache setup completed, link it into the list */
list_add(&cachep->next, &cache_chain);
- unlock_cpu_hotplug();
oops:
if (!cachep && (flags & SLAB_PANIC))
panic("kmem_cache_create(): failed to create slab `%s'\n",
name);
mutex_unlock(&cache_chain_mutex);
+ unlock_cpu_hotplug();
return cachep;
}
EXPORT_SYMBOL(kmem_cache_create);

2006-02-10 07:55:27

by Pekka Enberg

Subject: Re: [patch] slab: Avoid deadlock at kmem_cache_create/kmem_cache_destroy

On Thu, 9 Feb 2006, Ravikiran G Thirumalai wrote:
> Prevents deadlock situation between kmem_cache_create()/kmem_cache_destory(),
> and kmem_cache_create() /cpu hotplug. The locking order probably got
> moved over time.

Looks good to me.

Pekka