Is not locking task_lock in cgroup_fork() safe?

Li Zefan lizefan at
Fri Oct 19 08:50:34 UTC 2012

On 2012/10/19 8:58, Tejun Heo wrote:
> Hello, again.
> On Thu, Oct 18, 2012 at 05:38:35PM -0700, Tejun Heo wrote:
>> Even if there isn't an actual race, the comment is dead wrong.  I'm
>> reverting the following three patches.  Let's try again later.
>>   7e381b0eb1 ("cgroup: Drop task_lock(parent) on cgroup_fork()")
>>   7e3aa30ac8 ("cgroup: Remove task_lock() from cgroup_post_fork()")
> So, after some more looking, I think the following is correct and
> doesn't need to be reverted.  It's depending on threadgroup locking
> from migration path to synchronize against exit path which is always
> performed.
>>   c84cdf75cc ("cgroup: Remove unnecessary task_lock before fetching css_set on migration")
> Frederic, were you trying to say that the above commit is correct?
> Li, do you agree?

This one does look innocent.

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