On Tue, 28 Jul 2020, qiang.zhang@xxxxxxxxxxxxx wrote:
> From: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
>
> We should add node spinlock protect "n->alien" which may be
> assigned to NULL in cpuup_canceled func. cause address access
> exception.
>
Hi, do you have an example NULL pointer dereference where you have hit
this?
This rather looks like something to fix up in cpuup_canceled() since it's
currently manipulating the alien cache for the canceled cpu's node.
> Fixes: 18bf854117c6 ("slab: use get_node() and kmem_cache_node() functions")
> Signed-off-by: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
> ---
> 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
>
>
