From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f198.google.com (mail-it1-f198.google.com [209.85.166.198]) by kanga.kvack.org (Postfix) with ESMTP id BE8666B4996 for ; Tue, 27 Nov 2018 12:28:56 -0500 (EST) Received: by mail-it1-f198.google.com with SMTP id x82so27715053ita.9 for ; Tue, 27 Nov 2018 09:28:56 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id j187sor7509641itb.29.2018.11.27.09.28.55 for (Google Transport Security); Tue, 27 Nov 2018 09:28:55 -0800 (PST) MIME-Version: 1.0 References: <20181122165106.18238-1-daniel.vetter@ffwll.ch> <20181122165106.18238-4-daniel.vetter@ffwll.ch> <20181127074918.GT4266@phenom.ffwll.local> <154333737908.11623.17864230889834398136@skylake-alporthouse-com> In-Reply-To: <154333737908.11623.17864230889834398136@skylake-alporthouse-com> From: Daniel Vetter Date: Tue, 27 Nov 2018 18:28:43 +0100 Message-ID: Subject: Re: [Intel-gfx] [PATCH 3/3] mm, notifier: Add a lockdep map for invalidate_range_start Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Chris Wilson Cc: Linux Kernel Mailing List , Michal Hocko , Greg KH , intel-gfx , dri-devel , Linux MM , Jerome Glisse , Mike Rapoport , David Rientjes , Daniel Vetter , Andrew Morton , =?UTF-8?Q?Christian_K=C3=B6nig?= On Tue, Nov 27, 2018 at 5:50 PM Chris Wilson wro= te: > > Quoting Daniel Vetter (2018-11-27 07:49:18) > > On Thu, Nov 22, 2018 at 05:51:06PM +0100, 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 lockde= p > > > 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. > > > > > > Cc: Andrew Morton > > > Cc: David Rientjes > > > Cc: "J=C3=A9r=C3=B4me Glisse" > > > Cc: Michal Hocko > > > Cc: "Christian K=C3=B6nig" > > > Cc: Greg Kroah-Hartman > > > Cc: Daniel Vetter > > > Cc: Mike Rapoport > > > Cc: linux-mm@kvack.org > > > Signed-off-by: Daniel Vetter > > > > Any comments on this one here? This is really the main ingredient for > > catching deadlocks in mmu notifier callbacks. The other two patches are > > more the icing on the cake. > > > > Thanks, Daniel > > > > > --- > > > include/linux/mmu_notifier.h | 7 +++++++ > > > mm/mmu_notifier.c | 7 +++++++ > > > 2 files changed, 14 insertions(+) > > > > > > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifie= r.h > > > index 9893a6432adf..a39ba218dbbe 100644 > > > --- a/include/linux/mmu_notifier.h > > > +++ b/include/linux/mmu_notifier.h > > > @@ -12,6 +12,10 @@ struct mmu_notifier_ops; > > > > > > #ifdef CONFIG_MMU_NOTIFIER > > > > > > +#ifdef CONFIG_LOCKDEP > > > +extern struct lockdep_map __mmu_notifier_invalidate_range_start_map; > > > +#endif > > > + > > > /* > > > * The mmu notifier_mm structure is allocated and installed in > > > * mm->mmu_notifier_mm inside the mm_take_all_locks() protected > > > @@ -267,8 +271,11 @@ static inline void mmu_notifier_change_pte(struc= t mm_struct *mm, > > > static inline void mmu_notifier_invalidate_range_start(struct mm_str= uct *mm, > > > unsigned long start, unsigned long en= d) > > > { > > > + mutex_acquire(&__mmu_notifier_invalidate_range_start_map, 0, 0, > > > + _RET_IP_); > > Would not lock_acquire_shared() be more appropriate, i.e. treat this as > a rwsem_acquire_read()? read lock critical sections can't create any dependencies against any other read lock critical section of the same lock. Switching this to a read lock would just render the annotation pointless (if you don't include at least some write lock critical section somewhere, but I have no idea where you'd do that). A read lock that you only ever take for reading essentially doesn't do anything at all. So not clear on why you're suggesting this? It's the exact same idea like fs_reclaim of intserting a fake lock to tie all possible callchains to a given functions together with all possible callchains from that function. Of course this is only valid if all NxM combinations could happen in theory. For fs_reclaim that's true because direct reclaim can pick anything it wants to shrink/evict. For mmu notifier that's true as long as we assume any mmu notifier can be in use by any process, which only depends upon sufficiently contrived/evil userspace. I guess I could use lock_map_acquire/release() wrappers for this like fs_reclaim, would be a bit more clear. -Daniel --=20 Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch