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SubjectRe: [PATCH v2] zswap: only use CPU notifier when HOTPLUG_CPU=y
On Wed 30-11-16 13:15:16, Yu Zhao wrote:
> __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).
>
> v2: #ifdef for cpu_notifier_register_done during cleanup.

this ifedfery is just ugly as hell. I am also wondering whether it is
really needed. __register_cpu_notifier and __unregister_cpu_notifier are
noops for CONFIG_HOTPLUG_CPU=n. So what's exactly that is broken here?

> Signe-off-by: Yu Zhao <yuzhao@google.com>
> ---
> mm/zswap.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 275b22c..2915f44 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)
> {
> @@ -456,27 +459,34 @@ 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:
> for_each_online_cpu(cpu)
> __zswap_cpu_comp_notifier(pool, CPU_UP_CANCELED, cpu);
> +#ifdef CONFIG_HOTPLUG_CPU
> cpu_notifier_register_done();
> +#endif
> return -ENOMEM;
> }
>
> @@ -484,11 +494,15 @@ 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
>
> --
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--
Michal Hocko
SUSE Labs

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