linux-kernel - [RFC 17/17] drm/i915: Annotate dma_fence

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Date:   Tue, 12 May 2020 10:59:44 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     DRI Development <dri-devel@...ts.freedesktop.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        linux-rdma@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: [RFC 17/17] drm/i915: Annotate dma_fence_work

i915 does tons of allocations from this worker, which lockdep catches.

Also generic infrastructure like this with big potential for how
dma_fence or other cross driver contracts work, really should be
reviewed on dri-devel. Implementing custom wheels for everything
within the driver is a classic case of "platform problem" [1]. Which in
upstream we really shouldn't have.

Since there's no quick way to solve these splats (dma_fence_work is
used a bunch in basic buffer management and command submission) like
for amdgpu, I'm giving up at this point here. Annotating i915
scheduler and gpu reset could would be interesting, but since lockdep
is one-shot we can't see what surprises would lurk there.

1: https://lwn.net/Articles/443531/
Cc: linux-media@...r.kernel.org
Cc: linaro-mm-sig@...ts.linaro.org
Cc: linux-rdma@...r.kernel.org
Cc: amd-gfx@...ts.freedesktop.org
Cc: intel-gfx@...ts.freedesktop.org
Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: Christian König <christian.koenig@....com>
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
---
 drivers/gpu/drm/i915/i915_sw_fence_work.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_sw_fence_work.c b/drivers/gpu/drm/i915/i915_sw_fence_work.c
index a3a81bb8f2c3..5b74acadaef5 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence_work.c
+++ b/drivers/gpu/drm/i915/i915_sw_fence_work.c
@@ -17,12 +17,15 @@ static void fence_work(struct work_struct *work)
 {
 	struct dma_fence_work *f = container_of(work, typeof(*f), work);
 	int err;
+	bool fence_cookie;
 
+	fence_cookie = dma_fence_begin_signalling();
 	err = f->ops->work(f);
 	if (err)
 		dma_fence_set_error(&f->dma, err);
 
 	fence_complete(f);
+	dma_fence_end_signalling(fence_cookie);
 	dma_fence_put(&f->dma);
 }
 
-- 
2.26.2