Re: [PATCH 4/4] mm, notifier: Catch sleeping/blocking for !blockable

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Aug 20, 2019 at 05:18:10PM +0200, Daniel Vetter wrote:
> > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> > > index 538d3bb87f9b..856636d06ee0 100644
> > > +++ b/mm/mmu_notifier.c
> > > @@ -181,7 +181,13 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
> > >  	id = srcu_read_lock(&srcu);
> > >  	hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
> > >  		if (mn->ops->invalidate_range_start) {
> > > -			int _ret = mn->ops->invalidate_range_start(mn, range);
> > > +			int _ret;
> > > +
> > > +			if (!mmu_notifier_range_blockable(range))
> > > +				non_block_start();
> > > +			_ret = mn->ops->invalidate_range_start(mn, range);
> > > +			if (!mmu_notifier_range_blockable(range))
> > > +				non_block_end();
> > 
> > If someone Acks all the sched changes then I can pick this for
> > hmm.git, but I still think the existing pre-emption debugging is fine
> > for this use case.
> 
> Ok, I'll ping Peter Z. for an ack, iirc he was involved.
> 
> > Also, same comment as for the lockdep map, this needs to apply to the
> > non-blocking range_end also.
> 
> Hm, I thought the page table locks we're holding there already prevent any
> sleeping, so would be redundant?

AFAIK no. All callers of invalidate_range_start/end pairs do so a few
lines apart and don't change their locking in between - thus since
start can block so can end.

Would love to know if that is not true??

Similarly I've also been idly wondering if we should add a
'might_sleep()' to invalidate_rangestart/end() to make this constraint
clear & tested to the mm side?

Jason