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Date:   Tue, 20 Aug 2019 10:31:06 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Daniel Vetter <daniel.vetter@ffwll.ch>
Cc:     LKML <linux-kernel@vger.kernel.org>, Linux MM <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>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        Michal Hocko <mhocko@suse.com>,
        Christian =?utf-8?B?S8O2bmln?= <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 1/4] mm, notifier: Add a lockdep map for
 invalidate_range_start/end
Message-ID: <20190820133106.GE29246@ziepe.ca>
References: <20190820081902.24815-1-daniel.vetter@ffwll.ch>
 <20190820081902.24815-2-daniel.vetter@ffwll.ch>
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On Tue, Aug 20, 2019 at 10:18:59AM +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.
> 
> On Jason's suggestion this is is rolled out for both
> invalidate_range_start and invalidate_range_end. They both have the
> same calling context, hence we can share the same lockdep map. Note
> that the annotation for invalidate_ranage_start is outside of the
> mm_has_notifiers(), to make sure lockdep is informed about all paths
> leading to this context irrespective of whether mmu notifiers are
> present for a given context. We don't do that on the
> invalidate_range_end side to avoid paying the overhead twice, there
> the lockdep annotation is pushed down behind the mm_has_notifiers()
> check.
> 
> v2: Use lock_map_acquire/release() like fs_reclaim, to avoid confusion
> with this being a real mutex (Chris Wilson).
> 
> v3: Rebase on top of Glisse's arg rework.
> 
> v4: Also annotate invalidate_range_end (Jason Gunthorpe)
> Also annotate invalidate_range_start_nonblock, I somehow missed that
> one in the first version.
> 
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
> Cc: linux-mm@kvack.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  include/linux/mmu_notifier.h | 8 ++++++++
>  mm/mmu_notifier.c            | 9 +++++++++
>  2 files changed, 17 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>

Jason