| Re: [PATCH v5 2/2] decrement static keys on real destroy time [message #46401 is a reply to message #46399] |
Thu, 17 May 2012 10:18   |
KAMEZAWA Hiroyuki
Messages: 463
Registered: September 2006
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Senior Member |
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(2012/05/17 18:52), Glauber Costa wrote:
> On 05/17/2012 09:37 AM, Andrew Morton wrote:
>>>> If that happens, locking in static_key_slow_inc will prevent any damage.
>>>> My previous version had explicit code to prevent that, but we were
>>>> pointed out that this is already part of the static_key expectations, so
>>>> that was dropped.
>> This makes no sense. If two threads run that code concurrently,
>> key->enabled gets incremented twice. Nobody anywhere has a record that
>> this happened so it cannot be undone. key->enabled is now in an
>> unknown state.
>
> Kame, Tejun,
>
> Andrew is right. It seems we will need that mutex after all. Just this
> is not a race, and neither something that should belong in the
> static_branch interface.
>
Hmm....how about having
res_counter_xchg_limit(res, &old_limit, new_limit);
if (!cg_proto->updated && old_limit == RESOURCE_MAX)
....update labels...
Then, no mutex overhead maybe and activated will be updated only once.
Ah, but please fix in a way you like. Above is an example.
Thanks,
-Kame
(*) I'm sorry I won't be able to read e-mails, tomorrow.
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