linux-kernel - Re: [PATCH v8 3/4] cgroups: allow a cgroup subsystem to reject a fork

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Message-ID: <CAOviyai9dvCTGK=VUm0uDSo7XbmKk1BFDrRzL15ppAWf8YjG3w@mail.gmail.com>
Date:	Fri, 3 Apr 2015 10:42:27 +1100
From:	Aleksa Sarai <cyphar@...har.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, mingo@...hat.com, peterz@...radead.org,
	richard@....at,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v8 3/4] cgroups: allow a cgroup subsystem to reject a fork

Hello, Tejun.

>> +struct cgroup_fork_state {
>> +     void *ss_state[CGROUP_SUBSYS_COUNT];
>> +};
>
> Can we collect the subsystems which require pre/post fork callbacks to
> the front in group_subsys.h and do do CGROUP_SUBSYS_FORK_COUNT (or
> whatever) instead?  Then, we don't need all these subsys bitmasks
> either we can just test the index against that and be done with it.

I tried doing this and the kernel would refuse to boot. I believe it has
something to do with the ordering of early_init subsystems, but I'm not
entirely sure (this optimisation can be dealt with later [it's non-critical],
so IMO this should be done in a separate patchset [if at all]). Also, your
later comments would fix the subsys bitmask problem (we can just pass the
default %NULL), we don't even need to test the index.

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