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

[Li Zefan <lizefan@huawei.com>]

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.
>