On Fri, Dec 02, 2016 at 02:46:06PM +0100, Michal Hocko wrote:
> 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?
Well, I'm not a fan of ifdef and I don't like the unnecessary memory
usage (notifier_block) and lock (cpu_notifier_register_begin/done)
either.
Just pointing this out, having no problem living with your hotplug
fixes.
>
> > Signe-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> > ---
> > 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
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@xxxxxxxxx. For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
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>
> --
> Michal Hocko
> SUSE Labs
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