Is not locking task_lock in cgroup_fork() safe?

Tejun Heo tj at
Fri Oct 19 00:58:01 UTC 2012

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

>   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?



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