On 08/13/2014 12:19 PM, Oleg Nesterov wrote:
> On 08/13, Rik van Riel wrote:
>>
>> On 08/13/2014 11:58 AM, Oleg Nesterov wrote:
>>> On 08/13, Rik van Riel wrote:
>>>>
>>>> @@ -1017,7 +1017,7 @@ void __cleanup_sighand(struct sighand_struct
>>>> *sighand)
>>>> {
>>>> if (atomic_dec_and_test(&sighand->count)) {
>>>> signalfd_cleanup(sighand);
>>>> - kmem_cache_free(sighand_cachep, sighand);
>>>> + rcu_free(sighand_cachep, sighand);
>>>
>>> Please note that sighand_cachep is SLAB_DESTROY_BY_RCU.
>>
>> SLAB_DESTROY_BY_RCU means that the slab page is not given
>> back to the system until after the RCU grace period has
>> expired.
>>
>> However, the objects inside the slab can still be reused
>> immediately!
>
> Yes. This is fine. This memory won't be returned to system before rcu
> gp pass, and this memory is still "struct sighand_struct" with the
> properly initialized ->siglock (note the sighand_ctor()).
Fair enough, you are right.
The sighand_ctor does prevent any issues.
The slub code also prevents slubs with constructor
functions from ever getting merged, so this is all
taken care of.
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