On Tue, Apr 16, 2013 at 09:07:20PM +0800, Xiao Guangrong wrote:
> On 04/16/2013 07:43 PM, Robin Holt wrote:
> > Argh. Taking a step back helped clear my head.
> >
> > For the -stable releases, I agree we should just go with your
> > revert-plus-hlist_del_init_rcu patch. I will give it a test
> > when I am in the office.
>
> Okay. Wait for your test report. Thank you in advance.
>
> >
> > For the v3.10 release, we should work on making this more
> > correct and completely documented.
>
> Better document is always welcomed.
>
> Double call ->release is not bad, like i mentioned it in the changelog:
>
> it is really rare (e.g, can not happen on kvm since mmu-notify is unregistered
> after exit_mmap()) and the later call of multiple ->release should be
> fast since all the pages have already been released by the first call.
>
> But, of course, it's great if you have a _light_ way to avoid this.
Getting my test environment set back up took longer than I would have liked.
Your patch passed. I got no NULL-pointer derefs.
How would you feel about adding the following to your patch?
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index deca874..ff2fd5f 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -157,6 +157,7 @@ struct mmu_notifier_ops {
struct mmu_notifier {
struct hlist_node hlist;
const struct mmu_notifier_ops *ops;
+ int released;
};
static inline int mm_has_notifiers(struct mm_struct *mm)
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 606777a..949704b 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -44,7 +44,8 @@ void __mmu_notifier_release(struct mm_struct *mm)
* ->release returns.
*/
id = srcu_read_lock(&srcu);
- hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
+ hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
+ int released;
/*
* if ->release runs before mmu_notifier_unregister it
* must be handled as it's the only way for the driver
@@ -52,8 +53,10 @@ void __mmu_notifier_release(struct mm_struct *mm)
* from establishing any more sptes before all the
* pages in the mm are freed.
*/
- if (mn->ops->release)
+ released = xchg(&mn->released, 1);
+ if (mn->ops->release && !released)
mn->ops->release(mn, mm);
+ }
srcu_read_unlock(&srcu, id);
spin_lock(&mm->mmu_notifier_mm->lock);
@@ -214,6 +217,7 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
mm->mmu_notifier_mm = mmu_notifier_mm;
mmu_notifier_mm = NULL;
}
+ mn->released = 0;
atomic_inc(&mm->mm_count);
/*
@@ -295,6 +299,7 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
* before freeing the pages.
*/
int id;
+ int released;
id = srcu_read_lock(&srcu);
/*
@@ -302,7 +307,8 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
* guarantee ->release is called before freeing the
* pages.
*/
- if (mn->ops->release)
+ released = xchg(&mn->released, 1);
+ if (mn->ops->release && !released)
mn->ops->release(mn, mm);
srcu_read_unlock(&srcu, id);
--
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