From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>
Cc: "DRI Development" <dri-devel@lists.freedesktop.org>,
linux-rdma <linux-rdma@vger.kernel.org>,
intel-gfx <intel-gfx@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
"Chris Wilson" <chris@chris-wilson.co.uk>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Christian König" <christian.koenig@amd.com>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>
Subject: Re: [RFC 02/17] dma-fence: basic lockdep annotations
Date: Thu, 28 May 2020 16:22:51 +0200 [thread overview]
Message-ID: <CAKMK7uHb-DTKqiBKbcKuVeWPmRBsnq2QjWXQ44oLDE=qxLVvJA@mail.gmail.com> (raw)
In-Reply-To: <81b3a3be-b818-9e7c-e93e-ecf161bec94c@shipmail.org>
On Thu, May 28, 2020 at 3:37 PM Thomas Hellström (Intel)
<thomas_os@shipmail.org> wrote:
>
> 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.
See cover letter, that's going to be done for next round. For this one
here I just wanted to showcase a bit how it's used in a few different
places, mostly selected to get as much feedback from across different
drivers. Hence e.g. annotating drm/scheduler.
> Otherwise for patch 2 and 3,
>
> Reviewed-by: Thomas Hellstrom <thomas.hellstrom@intel.com>
I think I'll just cc you for the next round with docs, so you can make
sure it looks ok :-)
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
next prev parent reply other threads:[~2020-05-28 14:23 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)
2020-05-28 14:22 ` Daniel Vetter [this message]
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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