Hello again, Linus.

On Sun, Nov 27, 2011 at 01:25:58PM -0800, Tejun Heo wrote:

The problem is that cred_guard_mutex uses _interruptible/_killable
operations and rwsem doesn't have them, so cred_guard_mutex can't be
easily replaced with write-locking group_rwsem.

If the two locks can't be merged, under the proposed scheme, while not
exactly pretty, both fork/exit and exec paths go through single
locking and only the ones which want stable threadgroup need to grab
both locks, so IMHO it is at least reasonable.

Any better ideas?

I agree that the proposed solution is rather ugly but stable
thread-group is a valid mechanism to have and cgroup can benefit a lot
from it.  I'd be happy to revamp the implementation if anyone can come
up with a better way and can add big fat comment stating that.  Until
something better comes up, would it be okay to stick with this
implementation?

Thanks.

-- 
tejun