memory hotplug: make kmem_cache_node for SLUB on memory online avoid panic

Fix a panic due to access NULL pointer of kmem_cache_node at discard_slab()
after memory online.

When memory online is called, kmem_cache_nodes are created for all SLUBs
for new node whose memory are available.

slab_mem_going_online_callback() is called to make kmem_cache_node() in
callback of memory online event.  If it (or other callbacks) fails, then
slab_mem_offline_callback() is called for rollback.

In memory offline, slab_mem_going_offline_callback() is called to shrink
all slub cache, then slab_mem_offline_callback() is called later.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: locking fix]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 118 insertions, 0 deletions

diff --git a/mm/slub.c b/mm/slub.c
index e29a42988c78..aac1dd3c657d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -20,6 +20,7 @@
 #include <linux/mempolicy.h>
 #include <linux/ctype.h>
 #include <linux/kallsyms.h>
+#include <linux/memory.h>
 
 /*
  * Lock order:
@@ -2694,6 +2695,121 @@ int kmem_cache_shrink(struct kmem_cache *s)
 }
 EXPORT_SYMBOL(kmem_cache_shrink);
 
+#if defined(CONFIG_NUMA) && defined(CONFIG_MEMORY_HOTPLUG)
+static int slab_mem_going_offline_callback(void *arg)
+{
+        struct kmem_cache *s;
+
+        down_read(&slub_lock);
+        list_for_each_entry(s, &slab_caches, list)
+                kmem_cache_shrink(s);
+        up_read(&slub_lock);
+
+        return 0;
+}
+
+static void slab_mem_offline_callback(void *arg)
+{
+        struct kmem_cache_node *n;
+        struct kmem_cache *s;
+        struct memory_notify *marg = arg;
+        int offline_node;
+
+        offline_node = marg->status_change_nid;
+
+        /*
+         * If the node still has available memory. we need kmem_cache_node
+         * for it yet.
+         */
+        if (offline_node < 0)
+                return;
+
+        down_read(&slub_lock);
+        list_for_each_entry(s, &slab_caches, list) {
+                n = get_node(s, offline_node);
+                if (n) {
+                        /*
+                         * if n->nr_slabs > 0, slabs still exist on the node
+                         * that is going down. We were unable to free them,
+                         * and offline_pages() function shoudn't call this
+                         * callback. So, we must fail.
+                         */
+                        BUG_ON(atomic_read(&n->nr_slabs));
+
+                        s->node[offline_node] = NULL;
+                        kmem_cache_free(kmalloc_caches, n);
+                }
+        }
+        up_read(&slub_lock);
+}
+
+static int slab_mem_going_online_callback(void *arg)
+{
+        struct kmem_cache_node *n;
+        struct kmem_cache *s;
+        struct memory_notify *marg = arg;
+        int nid = marg->status_change_nid;
+        int ret = 0;
+
+        /*
+         * If the node's memory is already available, then kmem_cache_node is
+         * already created. Nothing to do.
+         */
+        if (nid < 0)
+                return 0;
+
+        /*
+         * We are bringing a node online. No memory is availabe yet. We must
+         * allocate a kmem_cache_node structure in order to bring the node
+         * online.
+         */
+        down_read(&slub_lock);
+        list_for_each_entry(s, &slab_caches, list) {
+                /*
+                 * XXX: kmem_cache_alloc_node will fallback to other nodes
+                 *      since memory is not yet available from the node that
+                 *      is brought up.
+                 */
+                n = kmem_cache_alloc(kmalloc_caches, GFP_KERNEL);
+                if (!n) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+                init_kmem_cache_node(n);
+                s->node[nid] = n;
+        }
+out:
+        up_read(&slub_lock);
+        return ret;
+}
+
+static int slab_memory_callback(struct notifier_block *self,
+                                unsigned long action, void *arg)
+{
+        int ret = 0;
+
+        switch (action) {
+        case MEM_GOING_ONLINE:
+                ret = slab_mem_going_online_callback(arg);
+                break;
+        case MEM_GOING_OFFLINE:
+                ret = slab_mem_going_offline_callback(arg);
+                break;
+        case MEM_OFFLINE:
+        case MEM_CANCEL_ONLINE:
+                slab_mem_offline_callback(arg);
+                break;
+        case MEM_ONLINE:
+        case MEM_CANCEL_OFFLINE:
+                break;
+        }
+
+        ret = notifier_from_errno(ret);
+        return ret;
+}
+
+#endif /* CONFIG_MEMORY_HOTPLUG */
+
 /********************************************************************
  *                      Basic setup of slabs
  *******************************************************************/
@@ -2715,6 +2831,8 @@ void __init kmem_cache_init(void)
                 sizeof(struct kmem_cache_node), GFP_KERNEL);
         kmalloc_caches[0].refcount = -1;
         caches++;
+
+        hotplug_memory_notifier(slab_memory_callback, 1);
 #endif
 
         /* Able to allocate the per node structures */