On Thu, Sep 01, 2011 at 08:22:21PM +0900, Tejun Heo wrote: > Hello, > > On Wed, Aug 31, 2011 at 03:42:24PM +0200, Frederic Weisbecker wrote: > > My task counter subsystem patchset brings a cancel_attach_task() callback > > that cancels can_attach_task() effects. > > > > I thought that rebased on top of your patch it's going to be merged inside > > cancel_attach() but OTOH we can't cancel the effect of failed migration > > on a thread that way. > > > > May be we need to keep a cancel_attach_task() just for that purpose? > > We can do that but I think that becomes a bit too complex and fragile. > That path won't be traveled unless it races against exit. Bugs will > be difficult to detect and reproduce. In this respect, the current > code already seems racy. ->can_attach (or other methods in the attach > path) and ->exit can race each other and I don't think all subsystems > handle that properly. I guess subsystems don't care about that currently, although I haven't checked. But the task counter will need this per thread cancellation in migration failure, without the need for any synchronization between can_attach, attach and exit. Now if we want to solve this with a synchronization there, either we task_lock() every tasks in the group in the beginning of cgroup_attach_proc(). But that's not very nice. Or we use cgroup_mutex on cgroup_exit() exit, but that's even worse. I guess we need the leader->sighand->siglock on both cgroup_attach_proc() and cgroup_exit(). Besides we may have more reasons to have that: https://lkml.org/lkml/2011/8/15/342 > > IMHO the right thing to do here is simplifying synchronization rules > so that nothing else happens while migration is in progress. > > Thanks. > > -- > tejun _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
