linux-kernel - Re: [PATCH 2/2] cpuset: remove redundant checks in file write functions

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Date:	Wed, 14 Aug 2013 10:01:32 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH 2/2] cpuset: remove redundant checks in file write functions

On 2013/8/13 23:05, Tejun Heo wrote:
> On Tue, Aug 13, 2013 at 09:17:53AM +0800, Li Zefan wrote:
>> Now cgroup core gets a reference to the css when a cgroup file is
>> opened(), and the reference is dropped at file release. so it's
>> guaranteed the cpuset is online during the write function.
> 
> Hmmm... it doesn't really guarantee that as css's can be offlined with
> residual css refcnts, os the css may well be offlined by the time it
> reaches the rw functions.  What's guaranteed is that their refcnts
> wouldn't be zero.

Oh, right.

But most controllers don't check this in those read/write functions.
It shoudn't do any harm not checking online/offline status.

> Eventually we need to implement proper sever
> semantics (probably by replacing the custom fs implementation with
> sysfs) but right now controllers still need to deal with offline
> css's.
> 
> Thanks.
> 

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