[PATCH v3] mm/slab.c: add node spinlock protect in __cache_free_alien

[qiang.zhang]

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

for example:
                                node0
        cpu0                                            cpu1
slab_dead_cpu
   >mutex_lock(&slab_mutex)
     >cpuup_canceled                            slab_dead_cpu
       >mask = cpumask_of_node(node)               >mutex_lock(&slab_mutex)
       >n = get_node(cachep0, node0)
       >spin_lock_irq(n&->list_lock)
       >if (!cpumask_empty(mask)) == true
        >spin_unlock_irq(&n->list_lock)
        >goto free_slab
       ....
   >mutex_unlock(&slab_mutex)

....                                               >cpuup_canceled
                                                     >mask = 
cpumask_of_node(node)
kmem_cache_free(cachep0 )                            >n = get_node(cachep0, 
node0)
 >__cache_free_alien(cachep0 )                       
 >>spin_lock_irq(n&->list_lock)
   >n = get_node(cachep0, node0)                     >if (!cpumask_empty(mask)) 
== false
   >if (n->alien && n->alien[page_node])             >alien = n->alien
     >alien = n->alien[page_node]                    >n->alien = NULL
     >....                                           
>spin_unlock_irq(&n->list_lock)
                                                     >....

Due to multiple cpu offline, The same cache in a node may be operated in
parallel,the "n->alien" should be protect.

Fixes: 6731d4f12315 ("slab: Convert to hotplug state machine")
Signed-off-by: Zhang Qiang <qiang.zh...@windriver.com>
---
 v1->v2->v3:
 change submission information and fixes tags.

 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