Messages in this thread | | | Date | Mon, 18 Feb 2013 12:36:13 +0200 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2] cgroup: fix cgroup_rmdir() vs close(eventfd) race |
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On Mon, Feb 18, 2013 at 02:12:23PM +0800, Li Zefan wrote: > commit 205a872bd6f9a9a09ef035ef1e90185a8245cc58 ("cgroup: fix lockdep > warning for event_control") solved a deadlock by introducing a new > bug. > > Move cgrp->event_list to a temporary list doesn't mean you can traverse > this list locklessly, because at the same time cgroup_event_wake() can > be called and remove the event from the list. The result of this race > is disastrous. > > We adopt the way how kvm irqfd code implements race-free event removal, > which is now described in the comments in cgroup_event_wake(). > > Signed-off-by: Li Zefan <lizefan@huawei.com> > --- > kernel/cgroup.c | 50 ++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 34 insertions(+), 16 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 26c071c..65c8101 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -217,6 +217,10 @@ struct cgroup_event { > */ > struct list_head list; > /* > + * Need to notify userspace when this event is removed? > + */ > + bool signal_on_remove; > + /* > * All fields below needed to unregister event when > * userspace closes eventfd. > */ > @@ -3833,8 +3837,17 @@ static void cgroup_event_remove(struct work_struct *work) > remove); > struct cgroup *cgrp = event->cgrp; > > + remove_wait_queue(event->wqh, &event->wait); > + > event->cft->unregister_event(cgrp, event->cft, event->eventfd); > > + /* > + * If this event is to be removed due to cgroup removal, > + * we notify userspace. > + */ > + if (event->signal_on_remove) > + eventfd_signal(event->eventfd, 1);
It's safe to notify anyway, isn't it? Let's just drop signal_on_remove.
Otherwise, look good.
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
-- Kirill A. Shutemov
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