From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by kanga.kvack.org (Postfix) with ESMTP id 6CC3F6B499E for ; Tue, 27 Nov 2018 12:34:33 -0500 (EST) Received: by mail-wm1-f69.google.com with SMTP id p16so16973764wmc.5 for ; Tue, 27 Nov 2018 09:34:33 -0800 (PST) Received: from fireflyinternet.com (mail.fireflyinternet.com. [109.228.58.192]) by mx.google.com with ESMTPS id w18si3083248wrr.154.2018.11.27.09.34.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Nov 2018 09:34:31 -0800 (PST) Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Chris Wilson In-Reply-To: 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> Message-ID: <154334003817.11623.5449603736660799102@skylake-alporthouse-com> Subject: Re: [Intel-gfx] [PATCH 3/3] mm, notifier: Add a lockdep map for invalidate_range_start Date: Tue, 27 Nov 2018 17:33:58 +0000 Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Vetter 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?= Quoting Daniel Vetter (2018-11-27 17:28:43) > On Tue, Nov 27, 2018 at 5:50 PM Chris Wilson w= rote: > > > > 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 lock= dep > > > > 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 roll= ed > > > > 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 a= re > > > 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_notif= ier.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_ma= p; > > > > +#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(str= uct mm_struct *mm, > > > > static inline void mmu_notifier_invalidate_range_start(struct mm_s= truct *mm, > > > > unsigned long start, unsigned long = end) > > > > { > > > > + 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? Just that it's not acting as a mutex, so emulating one looks wrong. -Chris