Re: [PATCH] cgroup: missing rcu read lock around task_css_set

[Sasha Levin]

On 03/04/2014 07:57 PM, Li Zefan wrote:
> On 2014/3/5 3:47, Tejun Heo wrote:
> > On Tue, Mar 04, 2014 at 12:20:45PM -0500, Sasha Levin wrote:
> > > > Hrm... there is a PF_EXITING check there already:
> > > >
> > > >      #define task_css_set_check(task, __c)            \
> > > >          rcu_dereference_check((task)->cgroups,        \
> > > >          lockdep_is_held(&cgroup_mutex) ||        \
> > > >          lockdep_is_held(&css_set_rwsem) ||        \
> > > >          ((task)->flags & PF_EXITING) || (__c))
> > > >
> > > > I see it's not happening on Linus's master so I'll run a bisection to figure out what broke it.
> > >
> > > Hi Tejun,
> > >
> > > It bisects down to your patch: "cgroup: drop task_lock() protection
> > > around task->cgroups". I'll look into it later unless it's obvious
> > > to you.
> >
> > Hmmm... maybe I'm confused and PF_EXITING is not set there and
> > task_lock was what held off the lockdep warning.  Confused....
>
> Because this cgroup_exit() is called in a failure path in copy_process().

It seems there was no conclusion here and it still happens in -next, anything
we can do about it?

Thanks,
Sasha

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