[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 <kiran@scalex86.org>
Signed-off-by: Shai Fultheim <shai@scalex86.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/mm/slab.c b/mm/slab.c
index d66c2b0d9715..add05d808a4a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1717,6 +1717,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
                 BUG();
         }
 
+        /*
+         * Prevent CPUs from coming and going.
+         * lock_cpu_hotplug() nests outside cache_chain_mutex
+         */
+        lock_cpu_hotplug();
+
         mutex_lock(&cache_chain_mutex);
 
         list_for_each(p, &cache_chain) {
@@ -1918,8 +1924,6 @@ kmem_cache_create (const char *name, size_t size, size_t align,
         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 +1982,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
 
         /* 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);