On 24/07/09 12:02 +0200, Louis Rilling wrote:
> Hi Ben,
>
> On 23/07/09 20:22 -0700, Ben Blum wrote:
> > Makes procs file writable to move all threads by tgid at once
> >
> > This patch adds functionality that enables users to move all threads in a
> > threadgroup at once to a cgroup by writing the tgid to the 'cgroup.procs'
> > file. This current implementation makes use of a rwsem that's taken for
> > reading in the fork() path to prevent newly forking threads within the
> > threadgroup from "escaping" while moving is in progress.
> >
> > Signed-off-by: Ben Blum <bblum@xxxxxxxxxx>
>
[...]
> > +int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
> > +{
> > + int retval;
> > + struct cgroup_subsys *ss;
> > + struct cgroup *oldcgrp;
> > + struct css_set *oldcg;
> > + struct cgroupfs_root *root = cgrp->root;
> > + int subsys_id;
> > + /* threadgroup list cursor */
> > + struct task_struct *tsk;
> > + /*
> > + * we need to make sure we have css_sets for all the tasks we're
> > + * going to move -before- we actually start moving them, so that in
> > + * case we get an ENOMEM we can bail out before making any changes.
> > + */
> > + struct list_head newcg_list;
> > + struct cg_list_entry *cg_entry;
> > +
> > + /* first, make sure this came from a valid tgid */
> > + if (!thread_group_leader(leader))
> > + return -EINVAL;
> > + /*
> > + * check that we can legitimately attach to the cgroup.
> > + */
> > + for_each_subsys(root, ss) {
> > + if (ss->can_attach) {
> > + retval = ss->can_attach(ss, cgrp, leader);
> > + if (retval)
> > + return retval;
> > + }
> > }
>
> So the semantics of ->can_attach() becomes: if called for a thread group leader,
> the result should be valid for the whole thread group, even if only the thread
> group leader is being attached. This looks a bit fuzzy and thus not desirable.
> Why not checking ->can_attach() for all threads (and lock cgroup_fork_mutex
> earlier)?
Ok I've read the next patch. Patch 6 should really go before this one, both for
better understanding and safety.
Thanks,
Louis
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
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