From: Daniel Vetter <daniel@ffwll.ch>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Daniel Vetter" <daniel.vetter@ffwll.ch>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org,
"DRI Development" <dri-devel@lists.freedesktop.org>,
"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
"Chris Wilson" <chris@chris-wilson.co.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
"David Rientjes" <rientjes@google.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Michal Hocko" <mhocko@suse.com>,
"Christian König" <christian.koenig@amd.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start
Date: Thu, 15 Aug 2019 09:10:14 +0200 [thread overview]
Message-ID: <20190815071014.GC7444@phenom.ffwll.local> (raw)
In-Reply-To: <20190815000959.GD11200@ziepe.ca>
On Wed, Aug 14, 2019 at 09:09:59PM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 14, 2019 at 10:20:26PM +0200, Daniel Vetter wrote:
> > This is a similar idea to the fs_reclaim fake lockdep lock. It's
> > fairly easy to provoke a specific notifier to be run on a specific
> > range: Just prep it, and then munmap() it.
> >
> > A bit harder, but still doable, is to provoke the mmu notifiers for
> > all the various callchains that might lead to them. But both at the
> > same time is really hard to reliable hit, especially when you want to
> > exercise paths like direct reclaim or compaction, where it's not
> > easy to control what exactly will be unmapped.
> >
> > By introducing a lockdep map to tie them all together we allow lockdep
> > to see a lot more dependencies, without having to actually hit them
> > in a single challchain while testing.
> >
> > Aside: Since I typed this to test i915 mmu notifiers I've only rolled
> > this out for the invaliate_range_start callback. If there's
> > interest, we should probably roll this out to all of them. But my
> > undestanding of core mm is seriously lacking, and I'm not clear on
> > whether we need a lockdep map for each callback, or whether some can
> > be shared.
>
> I was thinking about doing something like this..
>
> IMHO only range_end needs annotation, the other ops are either already
> non-sleeping or only used by KVM.
This isnt' about sleeping, this is about locking loops. And the biggest
risk for that is from driver code, and at least hmm_mirror only has the
driver code callback on invalidate_range_start. Once thing I discovered
using this (and it would be really hard to spot, it's deeply neested) is
that i915 userptr.
Even if i915 userptr would use hmm_mirror (to fix the issue you mention
below), if we then switch the annotation to invalidate_range_end nothing
interesting would ever come from this. Well, the only thing it'd catch is
issues in hmm_mirror, but I think core mm review will catch that before it
reaches us :-)
> BTW, I have found it strange that i915 only uses
> invalidate_range_start. Not really sure how it is able to do
> that. Would love to know the answer :)
I suspect it's broken :-/ Our userptr is ... not the best. Part of the
motivation here.
> > Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > include/linux/mmu_notifier.h | 6 ++++++
> > mm/mmu_notifier.c | 7 +++++++
> > 2 files changed, 13 insertions(+)
> >
> > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> > index b6c004bd9f6a..9dd38c32fc53 100644
> > +++ b/include/linux/mmu_notifier.h
> > @@ -42,6 +42,10 @@ enum mmu_notifier_event {
> >
> > #ifdef CONFIG_MMU_NOTIFIER
> >
> > +#ifdef CONFIG_LOCKDEP
> > +extern struct lockdep_map __mmu_notifier_invalidate_range_start_map;
> > +#endif
>
> I wonder what the trade off is having a global map vs a map in each
> mmu_notifier_mm ?
Less reports, specifically no reports involving multiple different mmu
notifiers to build the entire chain. But I'm assuming it's possible to
combine them in one mm (kvm+gpu+infiniband in one process sounds like
something someone could reasonably do), and it will help to make sure
everyone follows the same rules.
>
> > /*
> > * The mmu notifier_mm structure is allocated and installed in
> > * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
> > @@ -310,10 +314,12 @@ static inline void mmu_notifier_change_pte(struct mm_struct *mm,
> > static inline void
> > mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
> > {
> > + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
> > if (mm_has_notifiers(range->mm)) {
> > range->flags |= MMU_NOTIFIER_RANGE_BLOCKABLE;
> > __mmu_notifier_invalidate_range_start(range);
> > }
> > + lock_map_release(&__mmu_notifier_invalidate_range_start_map);
> > }
>
> Also range_end should have this too - it has all the same
> constraints. I think it can share the map. So 'range_start_map' is
> probably not the right name.
>
> It may also make some sense to do a dummy acquire/release under the
> mm_take_all_locks() to forcibly increase map coverage and reduce the
> scenario complexity required to hit bugs.
>
> And if we do decide on the reclaim thing in my other email then the
> reclaim dependency can be reliably injected by doing:
>
> fs_reclaim_acquire();
> lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
> lock_map_release(&__mmu_notifier_invalidate_range_start_map);
> fs_reclaim_release();
>
> If I understand lockdep properly..
Ime fs_reclaim injects the mmu_notifier map here reliably as soon as
you've thrown out the first pagecache mmap on any process. That "make sure
we inject it quickly" is why the lockdep is _outside_ of the
mm_has_notifiers() check. So no further injection needed imo.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2019-08-15 7:10 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-14 20:20 [PATCH 0/5] hmm & mmu_notifier debug/lockdep annotations Daniel Vetter
2019-08-14 20:20 ` [PATCH 1/5] mm: Check if mmu notifier callbacks are allowed to fail Daniel Vetter
2019-08-14 22:14 ` Andrew Morton
2019-08-14 23:22 ` Jason Gunthorpe
2019-08-14 23:34 ` Ralph Campbell
2019-08-16 17:19 ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 2/5] kernel.h: Add non_block_start/end() Daniel Vetter
2019-08-14 20:45 ` Andrew Morton
2019-08-15 6:52 ` Daniel Vetter
2019-08-15 8:44 ` Michal Hocko
2019-08-15 13:04 ` Jason Gunthorpe
2019-08-15 13:12 ` Daniel Vetter
2019-08-15 14:37 ` Jason Gunthorpe
2019-08-15 14:43 ` Daniel Vetter
2019-08-15 15:10 ` Jason Gunthorpe
2019-08-15 16:25 ` Daniel Vetter
2019-08-15 17:35 ` Jason Gunthorpe
2019-08-15 17:39 ` Jerome Glisse
2019-08-15 18:01 ` Jason Gunthorpe
2019-08-15 18:27 ` Jerome Glisse
2019-08-15 18:57 ` Jason Gunthorpe
2019-08-15 16:32 ` Jerome Glisse
2019-08-15 17:16 ` Jason Gunthorpe
2019-08-15 17:21 ` Daniel Vetter
2019-08-15 17:35 ` Jerome Glisse
2019-08-15 13:24 ` Michal Hocko
2019-08-15 22:15 ` Andrew Morton
2019-08-16 8:24 ` Michal Hocko
2019-08-14 23:58 ` Jason Gunthorpe
2019-08-15 6:58 ` Daniel Vetter
2019-08-15 12:23 ` Jason Gunthorpe
2019-08-15 13:21 ` Michal Hocko
2019-08-15 14:12 ` Jason Gunthorpe
2019-08-15 16:00 ` Michal Hocko
2019-08-15 16:56 ` Jason Gunthorpe
2019-08-15 17:11 ` Jerome Glisse
2019-08-15 17:17 ` Jason Gunthorpe
2019-08-15 17:42 ` Michal Hocko
2019-08-15 17:57 ` Jerome Glisse
2019-08-15 18:24 ` Jason Gunthorpe
2019-08-15 19:05 ` Michal Hocko
2019-08-15 19:18 ` Jason Gunthorpe
2019-08-15 19:35 ` Michal Hocko
2019-08-15 20:13 ` Jason Gunthorpe
2019-08-16 8:10 ` Michal Hocko
2019-08-16 12:19 ` Jason Gunthorpe
2019-08-16 12:26 ` Michal Hocko
2019-08-15 20:16 ` [Intel-gfx] " Daniel Vetter
2019-08-15 20:27 ` Jason Gunthorpe
2019-08-15 20:49 ` Daniel Vetter
2019-08-16 1:00 ` Jason Gunthorpe
2019-08-16 6:20 ` Daniel Vetter
2019-08-16 12:12 ` Jason Gunthorpe
2019-08-16 14:11 ` Daniel Vetter
2019-08-16 14:38 ` Jason Gunthorpe
2019-08-16 16:36 ` Daniel Vetter
2019-08-16 16:54 ` Jason Gunthorpe
2019-08-16 8:27 ` Michal Hocko
2019-08-14 20:20 ` [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable Daniel Vetter
2019-08-15 0:00 ` Jason Gunthorpe
2019-08-15 7:02 ` Daniel Vetter
[not found] ` <20190815123556.GB21596@ziepe.ca>
2019-08-17 16:09 ` Daniel Vetter
2019-08-14 20:20 ` [PATCH 4/5] mm, notifier: Add a lockdep map for invalidate_range_start Daniel Vetter
2019-08-15 0:09 ` Jason Gunthorpe
2019-08-15 7:10 ` Daniel Vetter [this message]
2019-08-15 12:53 ` Jason Gunthorpe
2019-08-14 20:20 ` [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables errors Daniel Vetter
2019-08-15 0:11 ` Jason Gunthorpe
2019-08-15 7:14 ` Daniel Vetter
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