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Subject: Re: [PATCH v4] fork: free vmapped stacks in cache when cpus are offline
From: Hoeun Ryu <hoeun.ryu@gmail.com>
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Date: Sat, 11 Feb 2017 18:56:41 +0900
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>, Mateusz Guzik <mguzik@redhat.com>,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com
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To: Thomas Gleixner <tglx@linutronix.de>
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> On Feb 11, 2017, at 5:31 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> 
>> On Sat, 11 Feb 2017, Hoeun Ryu wrote:
>> #define NR_CACHED_STACKS 2
>> static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
>> +
>> +static int free_vm_stack_cache(unsigned int cpu)
>> +{
>> +    struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu);
>> +    int i;
>> +
>> +    for (i = 0; i < NR_CACHED_STACKS; i++) {
>> +        struct vm_struct *vm_stack = cached_vm_stacks[i];
>> +
>> +        if (!vm_stack)
>> +            continue;
>> +
>> +        vfree(vm_stack->addr);
>> +        cached_vm_stacks[i] = NULL;
>> +    }
>> +
>> +    return 0;
>> +}
>> #endif
>> 
>> static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
>> @@ -456,6 +474,11 @@ void __init fork_init(void)
>>    for (i = 0; i < UCOUNT_COUNTS; i++) {
>>        init_user_ns.ucount_max[i] = max_threads/2;
>>    }
>> +
>> +#ifdef CONFIG_VMAP_STACK
>> +    cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vmstack_cache",
>> +              NULL, free_vm_stack_cache);
>> +#endif
> 
> If you wrap that in vm_stack_cache_init() and have a stub for !VMAP_STACK
> (add an #else to the #ifdef VMAP_STACK section above) then you spare the
> ugly ifdef in fork_init()

OK. I will.

> Thanks,
> 
>    tglx