staging: zcache: fix crash on cpu remove

In the case that a cpu is taken offline before zcache_do_preload() is
ever called on the cpu, the per-cpu zcache_preloads structure will
be uninitialized.  In the CPU_DEAD case for zcache_cpu_notifier(),
kp->obj is not checked before calling kmem_cache_free() on it.
If it is NULL, a crash results.

This patch ensures that both kp->obj and kp->page are not NULL before
calling the respective free functions. In practice, just checking
one or the other should be sufficient since they are assigned together
in zcache_do_preload(), but I check both for safety.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index fbb4001..dae2f4e 100644 (file)
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -1357,8 +1357,14 @@ static int zcache_cpu_notifier(struct notifier_block *nb,
                        kp->objnodes[kp->nr - 1] = NULL;
                        kp->nr--;
                }
-               kmem_cache_free(zcache_obj_cache, kp->obj);
-               free_page((unsigned long)kp->page);
+               if (kp->obj) {
+                       kmem_cache_free(zcache_obj_cache, kp->obj);
+                       kp->obj = NULL;
+               }
+               if (kp->page) {
+                       free_page((unsigned long)kp->page);
+                       kp->page = NULL;
+               }
                break;
        default:
                break;