[PATCH] zswap: only use CPU notifier when HOTPLUG_CPU=y

[Yu Zhao]

__unregister_cpu_notifier() only removes registered notifier from its
linked list when CPU hotplug is configured. If we free registered CPU
notifier when HOTPLUG_CPU=n, we corrupt the linked list.

To fix the problem, we can either use a static CPU notifier that walks
through each pool or just simply disable CPU notifier when CPU hotplug
is not configured (which is perfectly safe because the code in question
is called after all possible CPUs are online and will remain online
until power off).

Signed-off-by: Yu Zhao <yuz...@google.com>
---
 mm/zswap.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 275b22c..d92d19a 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -118,7 +118,9 @@ struct zswap_pool {
        struct kref kref;
        struct list_head list;
        struct work_struct work;
+#ifdef CONFIG_HOTPLUG_CPU
        struct notifier_block notifier;
+#endif
        char tfm_name[CRYPTO_MAX_ALG_NAME];
 };
 
@@ -448,6 +450,7 @@ static int __zswap_cpu_comp_notifier(struct zswap_pool 
*pool,
        return NOTIFY_OK;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
 static int zswap_cpu_comp_notifier(struct notifier_block *nb,
                                   unsigned long action, void *pcpu)
 {
@@ -456,21 +459,26 @@ static int zswap_cpu_comp_notifier(struct notifier_block 
*nb,
 
        return __zswap_cpu_comp_notifier(pool, action, cpu);
 }
+#endif
 
 static int zswap_cpu_comp_init(struct zswap_pool *pool)
 {
        unsigned long cpu;
 
+#ifdef CONFIG_HOTPLUG_CPU
        memset(&pool->notifier, 0, sizeof(pool->notifier));
        pool->notifier.notifier_call = zswap_cpu_comp_notifier;
 
        cpu_notifier_register_begin();
+#endif
        for_each_online_cpu(cpu)
                if (__zswap_cpu_comp_notifier(pool, CPU_UP_PREPARE, cpu) ==
                    NOTIFY_BAD)
                        goto cleanup;
+#ifdef CONFIG_HOTPLUG_CPU
        __register_cpu_notifier(&pool->notifier);
        cpu_notifier_register_done();
+#endif
        return 0;
 
 cleanup:
@@ -484,11 +492,15 @@ static void zswap_cpu_comp_destroy(struct zswap_pool 
*pool)
 {
        unsigned long cpu;
 
+#ifdef CONFIG_HOTPLUG_CPU
        cpu_notifier_register_begin();
+#endif
        for_each_online_cpu(cpu)
                __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu);
+#ifdef CONFIG_HOTPLUG_CPU
        __unregister_cpu_notifier(&pool->notifier);
        cpu_notifier_register_done();
+#endif
 }
 
 /*********************************
-- 
2.8.0.rc3.226.g39d4020