From: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
DRI Development <dri-devel@lists.freedesktop.org>
Cc: linux-rdma@vger.kernel.org, intel-gfx@lists.freedesktop.org,
LKML <linux-kernel@vger.kernel.org>,
amd-gfx@lists.freedesktop.org,
"Chris Wilson" <chris@chris-wilson.co.uk>,
linaro-mm-sig@lists.linaro.org,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Christian König" <christian.koenig@amd.com>,
linux-media@vger.kernel.org
Subject: Re: [RFC 02/17] dma-fence: basic lockdep annotations
Date: Thu, 28 May 2020 15:36:56 +0200 [thread overview]
Message-ID: <81b3a3be-b818-9e7c-e93e-ecf161bec94c@shipmail.org> (raw)
In-Reply-To: <20200512085944.222637-3-daniel.vetter@ffwll.ch>
On 2020-05-12 10:59, Daniel Vetter wrote:
> 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.
>
> 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>
LGTM. Perhaps some in-code documentation on how to use the new functions
are called.
Otherwise for patch 2 and 3,
Reviewed-by: Thomas Hellstrom <thomas.hellstrom@intel.com>
next prev parent reply other threads:[~2020-05-28 13:43 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 8:59 [RFC 00/17] dma-fence lockdep annotations Daniel Vetter
2020-05-12 8:59 ` [RFC 01/17] dma-fence: add might_sleep annotation to _wait() Daniel Vetter
2020-05-12 9:08 ` Christian König
2020-06-02 9:45 ` Maarten Lankhorst
2020-05-12 8:59 ` [RFC 02/17] dma-fence: basic lockdep annotations Daniel Vetter
2020-05-12 12:09 ` Jason Gunthorpe
2020-05-12 12:57 ` Daniel Vetter
[not found] ` <158927426244.15653.14406159524439944950@build.alporthouse.com>
2020-05-12 9:08 ` Daniel Vetter
[not found] ` <158927519651.15653.17392305363363808831@build.alporthouse.com>
2020-05-13 8:30 ` Daniel Vetter
2020-05-25 15:41 ` Daniel Vetter
2020-05-26 10:00 ` Maarten Lankhorst
2020-05-28 13:36 ` Thomas Hellström (Intel) [this message]
2020-05-28 14:22 ` Daniel Vetter
2020-05-28 21:54 ` Luben Tuikov
2020-05-29 5:49 ` Daniel Vetter
2020-05-12 8:59 ` [RFC 03/17] dma-fence: prime " Daniel Vetter
2020-05-12 8:59 ` [RFC 04/17] drm/vkms: Annotate vblank timer Daniel Vetter
2020-05-12 8:59 ` [RFC 05/17] drm/vblank: Annotate with dma-fence signalling section Daniel Vetter
2020-05-12 8:59 ` [RFC 06/17] drm/atomic-helper: Add dma-fence annotations Daniel Vetter
2020-05-12 8:59 ` [RFC 07/17] drm/amdgpu: add dma-fence annotations to atomic commit path Daniel Vetter
2020-05-12 8:59 ` [RFC 08/17] drm/scheduler: use dma-fence annotations in main thread Daniel Vetter
2020-05-25 15:30 ` Daniel Vetter
2020-05-12 8:59 ` [RFC 09/17] drm/amdgpu: use dma-fence annotations in cs_submit() Daniel Vetter
2020-05-13 7:02 ` Christian König
2020-05-13 7:07 ` Daniel Vetter
2020-05-12 8:59 ` [RFC 10/17] drm/amdgpu: s/GFP_KERNEL/GFP_ATOMIC in scheduler code Daniel Vetter
2020-05-12 15:56 ` Christian König
2020-05-12 16:20 ` Daniel Vetter
2020-05-12 16:27 ` Daniel Vetter
2020-05-12 17:31 ` Christian König
2020-05-12 18:34 ` Daniel Vetter
2020-05-12 8:59 ` [RFC 11/17] drm/amdgpu: DC also loves to allocate stuff where it shouldn't Daniel Vetter
2020-05-12 8:59 ` [RFC 12/17] drm/amdgpu/dc: Stop dma_resv_lock inversion in commit_tail Daniel Vetter
2020-05-12 8:59 ` [RFC 13/17] drm/scheduler: use dma-fence annotations in tdr work Daniel Vetter
2020-05-12 8:59 ` [RFC 14/17] drm/amdgpu: use dma-fence annotations for gpu reset code Daniel Vetter
2020-05-12 8:59 ` [RFC 15/17] Revert "drm/amdgpu: add fbdev suspend/resume on gpu reset" Daniel Vetter
2020-05-12 8:59 ` [RFC 16/17] drm/amdgpu: gpu recovery does full modesets Daniel Vetter
2020-05-12 12:54 ` Alex Deucher
2020-05-12 12:58 ` Daniel Vetter
2020-05-12 13:12 ` Alex Deucher
2020-05-12 13:17 ` Daniel Vetter
2020-05-12 13:29 ` Alex Deucher
2020-05-12 13:45 ` Daniel Vetter
2020-05-12 14:24 ` Alex Deucher
2020-05-12 16:12 ` Daniel Vetter
2020-05-12 20:10 ` Kazlauskas, Nicholas
2020-05-13 6:02 ` Daniel Vetter
2020-05-12 8:59 ` [RFC 17/17] drm/i915: Annotate dma_fence_work Daniel Vetter
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