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From: Daniel Vetter <daniel@ffwll.ch>
To: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>
Cc: linux-rdma@vger.kernel.org,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Intel Graphics Development" <intel-gfx@lists.freedesktop.org>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	linaro-mm-sig@lists.linaro.org,
	"Thomas Hellstrom" <thomas.hellstrom@intel.com>,
	amd-gfx@lists.freedesktop.org,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Mika Kuoppala" <mika.kuoppala@intel.com>,
	"Christian König" <christian.koenig@amd.com>,
	linux-media@vger.kernel.org
Subject: Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations
Date: Thu, 11 Jun 2020 10:34:30 +0200
Message-ID: <20200611083430.GD20149@phenom.ffwll.local> (raw)
In-Reply-To: <b11c2140-1b9c-9013-d9bb-9eb2c1906710@shipmail.org>

On Thu, Jun 11, 2020 at 09:30:12AM +0200, Thomas Hellström (Intel) wrote:
> 
> On 6/4/20 10:12 AM, Daniel Vetter wrote:
> > Two in one go:
> > - it is allowed to call dma_fence_wait() while holding a
> >    dma_resv_lock(). This is fundamental to how eviction works with ttm,
> >    so required.
> > 
> > - it is allowed to call dma_fence_wait() from memory reclaim contexts,
> >    specifically from shrinker callbacks (which i915 does), and from mmu
> >    notifier callbacks (which amdgpu does, and which i915 sometimes also
> >    does, and probably always should, but that's kinda a debate). Also
> >    for stuff like HMM we really need to be able to do this, or things
> >    get real dicey.
> > 
> > Consequence is that any critical path necessary to get to a
> > dma_fence_signal for a fence must never a) call dma_resv_lock nor b)
> > allocate memory with GFP_KERNEL. Also by implication of
> > dma_resv_lock(), no userspace faulting allowed. That's some supremely
> > obnoxious limitations, which is why we need to sprinkle the right
> > annotations to all relevant paths.
> > 
> > The one big locking context we're leaving out here is mmu notifiers,
> > added in
> > 
> > commit 23b68395c7c78a764e8963fc15a7cfd318bf187f
> > Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Date:   Mon Aug 26 22:14:21 2019 +0200
> > 
> >      mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end
> > 
> > that one covers a lot of other callsites, and it's also allowed to
> > wait on dma-fences from mmu notifiers. But there's no ready-made
> > functions exposed to prime this, so I've left it out for now.
> > 
> > v2: Also track against mmu notifier context.
> > 
> > v3: kerneldoc to spec the cross-driver contract. Note that currently
> > i915 throws in a hard-coded 10s timeout on foreign fences (not sure
> > why that was done, but it's there), which is why that rule is worded
> > with SHOULD instead of MUST.
> > 
> > Also some of the mmu_notifier/shrinker rules might surprise SoC
> > drivers, I haven't fully audited them all. Which is infeasible anyway,
> > we'll need to run them with lockdep and dma-fence annotations and see
> > what goes boom.
> > 
> > v4: A spelling fix from Mika
> > 
> > Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> > Cc: Thomas Hellstrom <thomas.hellstrom@intel.com>
> > Cc: linux-media@vger.kernel.org
> > Cc: linaro-mm-sig@lists.linaro.org
> > Cc: linux-rdma@vger.kernel.org
> > Cc: amd-gfx@lists.freedesktop.org
> > Cc: intel-gfx@lists.freedesktop.org
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >   Documentation/driver-api/dma-buf.rst |  6 ++++
> >   drivers/dma-buf/dma-fence.c          | 41 ++++++++++++++++++++++++++++
> >   drivers/dma-buf/dma-resv.c           |  4 +++
> >   include/linux/dma-fence.h            |  1 +
> >   4 files changed, 52 insertions(+)
> 
> I still have my doubts about allowing fence waiting from within shrinkers.
> IMO ideally they should use a trywait approach, in order to allow memory
> allocation during command submission for drivers that
> publish fences before command submission. (Since early reservation object
> release requires that).

Yeah it is a bit annoying, e.g. for drm/scheduler I think we'll end up
with a mempool to make sure it can handle it's allocations.

> But since drivers are already waiting from within shrinkers and I take your
> word for HMM requiring this,

Yeah the big trouble is HMM and mmu notifiers. That's the really awkward
one, the shrinker one is a lot less established.

I do wonder whether the mmu notifier constraint should only be set when
mmu notifiers are enabled, since on a bunch of arm-soc gpu drivers that
stuff just doesn't matter. But I expect that sooner or later these arm
gpus will show up in bigger arm cores, where you might want to have kvm
and maybe device virtualization and stuff, and then you need mmu
notifiers.

Plus having a very clear and consistent cross-driver api contract is imo
better than leaving this up to drivers and then having incompatible
assumptions.

I've pinged a bunch of armsoc gpu driver people and ask them how much this
hurts, so that we have a clear answer. On x86 I don't think we have much
of a choice on this, with userptr in amd and i915 and hmm work in nouveau
(but nouveau I think doesn't use dma_fence in there). I think it'll take
us a while to really bottom out on this specific question here.
-Daniel


> 
> Reviewed-by: Thomas Hellström <thomas.hellstrom@intel.com>
> 
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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  reply index

Thread overview: 106+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04  8:12 [PATCH 00/18] dma-fence lockdep annotations, round 2 Daniel Vetter
2020-06-04  8:12 ` [PATCH 01/18] mm: Track mmu notifiers in fs_reclaim_acquire/release Daniel Vetter
2020-06-10 12:01   ` Thomas Hellström (Intel)
2020-06-10 12:25     ` [Intel-gfx] " Daniel Vetter
2020-06-10 19:41   ` [PATCH] " Daniel Vetter
2020-06-11 14:29     ` Jason Gunthorpe
2020-06-21 17:42     ` Qian Cai
2020-06-21 18:07       ` Daniel Vetter
2020-06-21 20:01         ` Daniel Vetter
2020-06-21 22:09           ` Qian Cai
2020-06-23 16:17           ` Qian Cai
2020-06-23 22:13             ` Daniel Vetter
2020-06-23 22:29               ` Qian Cai
2020-06-23 22:31       ` Dave Chinner
2020-06-23 22:36         ` Daniel Vetter
2020-06-21 17:00   ` [PATCH 01/18] " Qian Cai
2020-06-21 17:28     ` Daniel Vetter
2020-06-21 17:46       ` Qian Cai
2020-06-04  8:12 ` [PATCH 02/18] dma-buf: minor doc touch-ups Daniel Vetter
2020-06-10 13:07   ` Thomas Hellström (Intel)
2020-06-04  8:12 ` [PATCH 03/18] dma-fence: basic lockdep annotations Daniel Vetter
2020-06-04  8:57   ` Thomas Hellström (Intel)
2020-06-04  9:21     ` Daniel Vetter
2020-06-04  9:26       ` Chris Wilson
2020-06-04  9:36         ` [Intel-gfx] " Daniel Vetter
2020-06-05 13:29   ` [PATCH] " Daniel Vetter
2020-06-05 14:30     ` Thomas Hellström (Intel)
2020-06-11  9:57     ` Maarten Lankhorst
2020-06-10 14:21   ` [Intel-gfx] [PATCH 03/18] " Tvrtko Ursulin
2020-06-10 15:17     ` Daniel Vetter
2020-06-11 10:36       ` Tvrtko Ursulin
2020-06-11 11:29         ` Daniel Vetter
2020-06-11 14:29           ` Tvrtko Ursulin
2020-06-11 15:03             ` Daniel Vetter
2020-06-11  8:00   ` Chris Wilson
2020-06-11  8:44     ` Dave Airlie
2020-06-11  9:01       ` [Intel-gfx] " Daniel Stone
2020-06-19  8:25         ` Chris Wilson
2020-06-19  8:51           ` Daniel Vetter
2020-06-19  9:13             ` Chris Wilson
2020-06-19  9:43               ` Daniel Vetter
2020-06-19 13:12                 ` Chris Wilson
2020-06-22  9:16                   ` Daniel Vetter
2020-07-09  7:29                 ` Daniel Stone
2020-07-09  8:01                   ` Daniel Vetter
2020-06-12  7:06   ` [PATCH] " Daniel Vetter
2020-06-04  8:12 ` [PATCH 04/18] dma-fence: prime " Daniel Vetter
2020-06-11  7:30   ` [Linaro-mm-sig] " Thomas Hellström (Intel)
2020-06-11  8:34     ` Daniel Vetter [this message]
2020-06-11 14:15       ` Jason Gunthorpe
2020-06-11 23:35         ` Felix Kuehling
2020-06-12  5:11           ` Daniel Vetter
2020-06-19 18:13           ` Jerome Glisse
2020-06-23  7:39           ` Daniel Vetter
2020-06-23 18:44             ` Felix Kuehling
2020-06-23 19:02               ` Daniel Vetter
2020-06-16 12:07         ` Daniel Vetter
2020-06-16 14:53           ` Jason Gunthorpe
2020-06-17  7:57             ` Daniel Vetter
2020-06-17 15:29               ` Jason Gunthorpe
2020-06-18 14:42                 ` Daniel Vetter
2020-06-17  6:48           ` Daniel Vetter
2020-06-17 15:28             ` Jason Gunthorpe
2020-06-18 15:00               ` Daniel Vetter
2020-06-18 17:23                 ` Jason Gunthorpe
2020-06-19  7:22                   ` Daniel Vetter
2020-06-19 11:39                     ` Jason Gunthorpe
2020-06-19 15:06                       ` Daniel Vetter
2020-06-19 15:15                         ` Jason Gunthorpe
2020-06-19 16:19                           ` Daniel Vetter
2020-06-19 17:23                             ` Jason Gunthorpe
2020-06-19 18:09                               ` Jerome Glisse
2020-06-19 18:18                                 ` Jason Gunthorpe
2020-06-19 19:48                                   ` Felix Kuehling
2020-06-19 19:55                                     ` Jason Gunthorpe
2020-06-19 20:03                                       ` Felix Kuehling
2020-06-19 20:31                                       ` Jerome Glisse
2020-06-22 11:46                                         ` Jason Gunthorpe
2020-06-22 20:15                                           ` Jerome Glisse
2020-06-23  0:02                                             ` Jason Gunthorpe
2020-06-19 20:10                                   ` Jerome Glisse
2020-06-19 20:43                                     ` Daniel Vetter
2020-06-19 20:59                                       ` Jerome Glisse
2020-06-23  0:05                                     ` Jason Gunthorpe
2020-06-19 19:11                                 ` Alex Deucher
2020-06-19 19:30                                   ` Felix Kuehling
2020-06-19 19:40                                     ` Jerome Glisse
2020-06-19 19:51                                     ` Jason Gunthorpe
2020-06-12  7:01   ` [PATCH] " Daniel Vetter
2020-06-04  8:12 ` [PATCH 05/18] drm/vkms: Annotate vblank timer Daniel Vetter
2020-06-04  8:12 ` [PATCH 06/18] drm/vblank: Annotate with dma-fence signalling section Daniel Vetter
2020-06-04  8:12 ` [PATCH 07/18] drm/atomic-helper: Add dma-fence annotations Daniel Vetter
2020-06-04  8:12 ` [PATCH 08/18] drm/amdgpu: add dma-fence annotations to atomic commit path Daniel Vetter
2020-06-23 10:51   ` Daniel Vetter
2020-06-04  8:12 ` [PATCH 09/18] drm/scheduler: use dma-fence annotations in main thread Daniel Vetter
2020-06-04  8:12 ` [PATCH 10/18] drm/amdgpu: use dma-fence annotations in cs_submit() Daniel Vetter
2020-06-04  8:12 ` [PATCH 11/18] drm/amdgpu: s/GFP_KERNEL/GFP_ATOMIC in scheduler code Daniel Vetter
2020-06-04  8:12 ` [PATCH 12/18] drm/amdgpu: DC also loves to allocate stuff where it shouldn't Daniel Vetter
2020-06-04  8:12 ` [PATCH 13/18] drm/amdgpu/dc: Stop dma_resv_lock inversion in commit_tail Daniel Vetter
2020-06-05  8:30   ` Pierre-Eric Pelloux-Prayer
2020-06-05 12:41     ` Daniel Vetter
2020-06-04  8:12 ` [PATCH 14/18] drm/scheduler: use dma-fence annotations in tdr work Daniel Vetter
2020-06-04  8:12 ` [PATCH 15/18] drm/amdgpu: use dma-fence annotations for gpu reset code Daniel Vetter
2020-06-04  8:12 ` [PATCH 16/18] Revert "drm/amdgpu: add fbdev suspend/resume on gpu reset" Daniel Vetter
2020-06-04  8:12 ` [PATCH 17/18] drm/amdgpu: gpu recovery does full modesets Daniel Vetter
2020-06-04  8:12 ` [PATCH 18/18] drm/i915: Annotate dma_fence_work Daniel Vetter

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