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, 4 insertions, 0 deletions

diff --git a/include/linux/memory.h b/include/linux/memory.h
index ec376e482abb..33f0ff0cf634 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -83,10 +83,14 @@ extern int memory_notify(unsigned long val, void *v);
 
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
 
+#ifdef CONFIG_MEMORY_HOTPLUG
 #define hotplug_memory_notifier(fn, pri) {                      \
         static struct notifier_block fn##_mem_nb =              \
                 { .notifier_call = fn, .priority = pri };       \
         register_memory_notifier(&fn##_mem_nb);                 \
 }
+#else
+#define hotplug_memory_notifier(fn, pri) do { } while (0)
+#endif
 
 #endif /* _LINUX_MEMORY_H_ */