[PATCH] mm/slab.c: add node spinlock protect in __cache_free_alien

[qiang.zhang]

From: Zhang Qiang <qiang.zh...@windriver.com>

We should add node spinlock protect "n->alien" which may be
assigned to NULL in cpuup_canceled func. cause address access
exception.

Fixes: 18bf854117c6 ("slab: use get_node() and kmem_cache_node() functions")
Signed-off-by: Zhang Qiang <qiang.zh...@windriver.com>
---
 mm/slab.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index a89633603b2d..290523c90b4e 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -759,8 +759,10 @@ static int __cache_free_alien(struct kmem_cache *cachep, 
void *objp,
 
        n = get_node(cachep, node);
        STATS_INC_NODEFREES(cachep);
+       spin_lock(&n->list_lock);
        if (n->alien && n->alien[page_node]) {
                alien = n->alien[page_node];
+               spin_unlock(&n->list_lock);
                ac = &alien->ac;
                spin_lock(&alien->lock);
                if (unlikely(ac->avail == ac->limit)) {
@@ -769,14 +771,15 @@ static int __cache_free_alien(struct kmem_cache *cachep, 
void *objp,
                }
                ac->entry[ac->avail++] = objp;
                spin_unlock(&alien->lock);
-               slabs_destroy(cachep, &list);
        } else {
+               spin_unlock(&n->list_lock);
                n = get_node(cachep, page_node);
                spin_lock(&n->list_lock);
                free_block(cachep, &objp, 1, page_node, &list);
                spin_unlock(&n->list_lock);
-               slabs_destroy(cachep, &list);
        }
+
+       slabs_destroy(cachep, &list);
        return 1;
 }
 
-- 
2.26.2