From: Chris Wilson <chris@chris-wilson.co.uk>
To: DRI Development <dri-devel@lists.freedesktop.org>,
Daniel Vetter <daniel.vetter@ffwll.ch>
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>,
amd-gfx@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
Thomas Hellstrom <thomas.hellstrom@intel.com>,
Daniel Vetter <daniel.vetter@intel.com>,
linux-media@vger.kernel.org,
Christian König <christian.koenig@amd.com>,
Mika Kuoppala <mika.kuoppala@intel.com>
Subject: Re: [PATCH 03/18] dma-fence: basic lockdep annotations
Date: Thu, 11 Jun 2020 09:00:36 +0100 [thread overview]
Message-ID: <159186243606.1506.4437341616828968890@build.alporthouse.com> (raw)
In-Reply-To: <20200604081224.863494-4-daniel.vetter@ffwll.ch>
Quoting Daniel Vetter (2020-06-04 09:12:09)
> Design is similar to the lockdep annotations for workers, but with
> some twists:
>
> - We use a read-lock for the execution/worker/completion side, so that
> this explicit annotation can be more liberally sprinkled around.
> With read locks lockdep isn't going to complain if the read-side
> isn't nested the same way under all circumstances, so ABBA deadlocks
> are ok. Which they are, since this is an annotation only.
>
> - We're using non-recursive lockdep read lock mode, since in recursive
> read lock mode lockdep does not catch read side hazards. And we
> _very_ much want read side hazards to be caught. For full details of
> this limitation see
>
> commit e91498589746065e3ae95d9a00b068e525eec34f
> Author: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Aug 23 13:13:11 2017 +0200
>
> locking/lockdep/selftests: Add mixed read-write ABBA tests
>
> - To allow nesting of the read-side explicit annotations we explicitly
> keep track of the nesting. lock_is_held() allows us to do that.
>
> - The wait-side annotation is a write lock, and entirely done within
> dma_fence_wait() for everyone by default.
>
> - To be able to freely annotate helper functions I want to make it ok
> to call dma_fence_begin/end_signalling from soft/hardirq context.
> First attempt was using the hardirq locking context for the write
> side in lockdep, but this forces all normal spinlocks nested within
> dma_fence_begin/end_signalling to be spinlocks. That bollocks.
>
> The approach now is to simple check in_atomic(), and for these cases
> entirely rely on the might_sleep() check in dma_fence_wait(). That
> will catch any wrong nesting against spinlocks from soft/hardirq
> contexts.
>
> The idea here is that every code path that's critical for eventually
> signalling a dma_fence should be annotated with
> dma_fence_begin/end_signalling. The annotation ideally starts right
> after a dma_fence is published (added to a dma_resv, exposed as a
> sync_file fd, attached to a drm_syncobj fd, or anything else that
> makes the dma_fence visible to other kernel threads), up to and
> including the dma_fence_wait(). Examples are irq handlers, the
> scheduler rt threads, the tail of execbuf (after the corresponding
> fences are visible), any workers that end up signalling dma_fences and
> really anything else. Not annotated should be code paths that only
> complete fences opportunistically as the gpu progresses, like e.g.
> shrinker/eviction code.
>
> The main class of deadlocks this is supposed to catch are:
>
> Thread A:
>
> mutex_lock(A);
> mutex_unlock(A);
>
> dma_fence_signal();
>
> Thread B:
>
> mutex_lock(A);
> dma_fence_wait();
> mutex_unlock(A);
>
> Thread B is blocked on A signalling the fence, but A never gets around
> to that because it cannot acquire the lock A.
>
> Note that dma_fence_wait() is allowed to be nested within
> dma_fence_begin/end_signalling sections. To allow this to happen the
> read lock needs to be upgraded to a write lock, which means that any
> other lock is acquired between the dma_fence_begin_signalling() call and
> the call to dma_fence_wait(), and still held, this will result in an
> immediate lockdep complaint. The only other option would be to not
> annotate such calls, defeating the point. Therefore these annotations
> cannot be sprinkled over the code entirely mindless to avoid false
> positives.
>
> v2: handle soft/hardirq ctx better against write side and dont forget
> EXPORT_SYMBOL, drivers can't use this otherwise.
>
> v3: Kerneldoc.
>
> v4: Some spelling fixes 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>
Introducing a global lockmap that cannot capture the rules correctly,
Nacked-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris
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next prev parent reply other threads:[~2020-06-11 8:01 UTC|newest]
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 [this message]
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
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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