linux-kernel - Re: [PATCH 2/3] percpu counter: cast this_cpu

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Message-ID: <xr93ob6a1yl6.fsf@gthelen.mtv.corp.google.com>
Date:	Sun, 27 Oct 2013 09:13:25 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	handai.szj@...bao.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/3] percpu counter: cast this_cpu_sub() adjustment

On Sun, Oct 27 2013, Tejun Heo wrote:

> On Sun, Oct 27, 2013 at 05:04:29AM -0700, Andrew Morton wrote:
>> On Sun, 27 Oct 2013 07:22:55 -0400 Tejun Heo <tj@...nel.org> wrote:
>> 
>> > We probably want to cc stable for this and the next one.  How should
>> > these be routed?  I can take these through percpu tree or mm works
>> > too.  Either way, it'd be best to route them together.
>> 
>> Yes, all three look like -stable material to me.  I'll grab them later
>> in the week if you haven't ;)
>
> Tried to apply to percpu but the third one is a fix for a patch which
> was added to -mm during v3.12-rc1, so these are yours. :)

I don't object to stable for the first two non-memcg patches, but it's
probably unnecessary.  I should have made it more clear, but an audit of
v3.12-rc6 shows that only new memcg code is affected - the new
mem_cgroup_move_account_page_stat() is the only place where an unsigned
adjustment is used.  All other callers (e.g. shrink_dcache_sb) already
use a signed adjustment, so no problems before v3.12.  Though I did not
audit the stable kernel trees, so there could be something hiding in
there.

>> The names of the first two patches distress me.  They rather clearly
>> assert that the code affects percpu_counter.[ch], but that is not the case. 
>> Massaging is needed to fix that up.
>
> Yeah, something like the following would be better
>
>  percpu: add test module for various percpu operations
>  percpu: fix this_cpu_sub() subtrahend casting for unsigneds
>  memcg: use __this_cpu_sub() to dec stats to avoid incorrect subtrahend casting

No objection to renaming.  Let me know if you want these reposed with
updated titles.
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