Nouveau currently relies on the assumption that dma_fences will only
ever get signalled through nouveau_fence_signal(), which takes care of
removing a signalled fence from the list nouveau_fence_chan.pending.
This self-imposed rule is violated in nouveau_fence_done(), where
dma_fence_is_signaled() can signal the fence without removing it from
the list. This enables accesses to already signalled fences through the
list, which is a bug.
Furthermore, it must always be possible to use standard dma_fence
methods an a dma_fence and observe valid behavior. The canonical way of
ensuring that signalling a fence has additional effects is to add those
effects to a callback and register it on the fence.
Move the code from nouveau_fence_signal() into a dma_fence callback.
Register that callback when creating the fence.
Cc: <sta...@vger.kernel.org> # 4.10+
Fixes: f54d1867005c ("dma-buf: Rename struct fence to dma_fence")
Signed-off-by: Philipp Stanner <pha...@kernel.org>
---
I'm not entirely sure what Fixes-Tag is appropriate. The last time the
line causing the signalled fence in the list was touched is the commit
listed above.
---
drivers/gpu/drm/nouveau/nouveau_fence.c | 41 ++++++++++++++++---------
drivers/gpu/drm/nouveau/nouveau_fence.h | 1 +
2 files changed, 27 insertions(+), 15 deletions(-)
diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c
b/drivers/gpu/drm/nouveau/nouveau_fence.c
index 7cc84472cece..b2c2241a8803 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -50,24 +50,22 @@ nouveau_fctx(struct nouveau_fence *fence)
return container_of(fence->base.lock, struct nouveau_fence_chan, lock);
}
-static int
-nouveau_fence_signal(struct nouveau_fence *fence)
+static void
+nouveau_fence_cleanup_cb(struct dma_fence *dfence, struct dma_fence_cb *cb)
{
- int drop = 0;
+ struct nouveau_fence_chan *fctx;
+ struct nouveau_fence *fence;
+
+ fence = container_of(dfence, struct nouveau_fence, base);
+ fctx = nouveau_fctx(fence);
- dma_fence_signal_locked(&fence->base);
list_del(&fence->head);
rcu_assign_pointer(fence->channel, NULL);
- if (test_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags)) {
- struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
-
- if (!--fctx->notify_ref)
- drop = 1;
- }
+ if (test_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags))
+ --fctx->notify_ref;
dma_fence_put(&fence->base);
- return drop;
}
static struct nouveau_fence *
@@ -93,7 +91,8 @@ nouveau_fence_context_kill(struct nouveau_fence_chan *fctx,
int error)
if (error)
dma_fence_set_error(&fence->base, error);
- if (nouveau_fence_signal(fence))
+ dma_fence_signal_locked(&fence->base);
+ if (fctx->notify_ref == 0)
nvif_event_block(&fctx->event);
}
fctx->killed = 1;
@@ -131,7 +130,6 @@ static int
nouveau_fence_update(struct nouveau_channel *chan, struct nouveau_fence_chan
*fctx)
{
struct nouveau_fence *fence;
- int drop = 0;
u32 seq = fctx->read(chan);
while (!list_empty(&fctx->pending)) {
@@ -140,10 +138,10 @@ nouveau_fence_update(struct nouveau_channel *chan, struct
nouveau_fence_chan *fc
if ((int)(seq - fence->base.seqno) < 0)
break;
- drop |= nouveau_fence_signal(fence);
+ dma_fence_signal_locked(&fence->base);
}
- return drop;
+ return fctx->notify_ref == 0 ? 1 : 0;
}
static void
@@ -235,6 +233,19 @@ nouveau_fence_emit(struct nouveau_fence *fence)
&fctx->lock, fctx->context, ++fctx->sequence);
kref_get(&fctx->fence_ref);
+ fence->cb.func = nouveau_fence_cleanup_cb;
+ /* Adding a callback runs into __dma_fence_enable_signaling(), which
will
+ * ultimately run into nouveau_fence_no_signaling(), where a WARN_ON
+ * would fire because the refcount can be dropped there.
+ *
+ * Increment the refcount here temporarily to work around that.
+ */
+ dma_fence_get(&fence->base);
+ ret = dma_fence_add_callback(&fence->base, &fence->cb,
nouveau_fence_cleanup_cb);
+ dma_fence_put(&fence->base);
+ if (ret)
+ return ret;
+
ret = fctx->emit(fence);
if (!ret) {
dma_fence_get(&fence->base);
diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h
b/drivers/gpu/drm/nouveau/nouveau_fence.h
index 8bc065acfe35..e6b2df7fdc42 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.h
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
@@ -10,6 +10,7 @@ struct nouveau_bo;
struct nouveau_fence {
struct dma_fence base;
+ struct dma_fence_cb cb;
struct list_head head;
--
2.48.1
