linux-kernel - Re: [PATCH v6 2/3] cgroups: allow a cgroup subsystem to reject a fork

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Date:	Fri, 27 Mar 2015 08:41:05 +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 v6 2/3] cgroups: allow a cgroup subsystem to reject a fork

Hi,

>> callback if the association changes [we could call it something else if you
>> like, since reapply_fork() is a pids-specific name -- what about switch_fork(),
>> reassoc_fork(), re_fork() or something to show that it's a callback if the
>> association changes?] (the subsystem can decide if they want to ignore it / if
>> they don't want to touch it) and we deal with pinning / dropping the ref of the
>> css_set for the current task inside the cgroup_* callbacks. That way, we don't
>> start messing around with post-fork() callbacks that aren't related to the new
>> conditional stuff.
>
> You can't pin css_set from inside cgroup callbacks.  It's a construct
> which in general shouldn't be accessible outside cgroup core.

Yeah, sorry I meant css (you aren't pinning, but you're still saving under RCU
and dealing with the association-related stuff inside post_fork).


>> I mean, if you want to have a random, completely unused and essentially
>> vestigial argument to ss->fork() [if you don't use the new can_fork() callbacks
>> (and actually care about storing private data)] then I can just write that. It
>> just looks like a weird callback API imho.
>
> It's an opaque token from pre.  If a subsys doesn't have pre, it's
> NULL.  I don't see anything weird about that, so let's please go that
> way.

Alright, if you think that's the best way. I still think it's weird, but I
guess that's probably just down to personal taste.


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