linux-kernel - Re: [PATCH v10 3/4] cgroups: allow a cgroup subsystem to reject a fork

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Date:	Thu, 14 May 2015 20:57:49 +1000
From:	Aleksa Sarai <cyphar@...har.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, mingo@...hat.com,
	Peter Zijlstra <peterz@...radead.org>, richard@....at,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v10 3/4] cgroups: allow a cgroup subsystem to reject a fork

Hi Tejun,

>> +/* Ditto for the can_fork/cancel_fork/reapply_fork callbacks. */
>> +static int need_canfork_callback __read_mostly;
>> +static int need_cancelfork_callback __read_mostly;
>
> And given that the reason we have these masks is avoiding iteration in
> relatively hot paths.  Does cancelfork mask make sense?

Do you still want me to remove it? I only added it because it made the
callback code more consistent for cancel_fork and can_fork.

>> +void cgroup_cancel_fork(struct task_struct *child,
>> +                     void *ss_state[CGROUP_PREFORK_COUNT])
>> +{
>> +     struct cgroup_subsys *ss;
>> +     int i;
>> +
>> +     for_each_subsys_which(need_cancelfork_callback, ss, i) {
>> +             void *state = NULL;
>> +
>> +             if (CGROUP_PREFORK_START <= i && i < CGROUP_PREFORK_END)
>> +                     state = ss_state[i - CGROUP_PREFORK_START];
>
> Maybe we want a helper callback which does
>
>         if (CGROUP_PREFORK_START <= ssid && ssid < CGROUP_PREFORK_END)
>                 return &ss_state[ssid - CGROUP_PREFORK_START];
>         return NULL;

What would be a nice name for it? I can't think of anything better
than __get_ss_private() and __get_ss_privatep().

--
Aleksa Sarai (cyphar)
www.cyphar.com
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