Messages in this thread | | | Date | Thu, 16 Feb 2012 16:39:48 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2/4] vfork: make it killable |
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On Thu, 16 Feb 2012 18:27:06 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
> --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -669,10 +669,34 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) > > void complete_vfork_done(struct task_struct *tsk) > { > - struct completion *vfork_done = tsk->vfork_done; > + struct completion *vfork; > > - tsk->vfork_done = NULL; > - complete(vfork_done); > + task_lock(tsk); > + vfork = tsk->vfork_done; > + if (likely(vfork)) { > + tsk->vfork_done = NULL; > + complete(vfork); > + } > + task_unlock(tsk); > +}
OK, so now we don't need to test tsk->vfork_done in callers. But mm_release() still does this, and it does it outside locks. Mistake, or micro-optimisation? If the latter, why is the lockless peek race-free?
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