drm/nouveau: Refactor context destruction to avoid a lock ordering issue.

The destroy_context() engine hooks call gpuobj management functions to
release the channel resources, these functions use HARDIRQ-unsafe locks
whereas destroy_context() is called with the HARDIRQ-safe
context_switch_lock held, that's a lock ordering violation.

Push the engine-specific channel destruction logic into destroy_context()
and let the hardware-specific code lock and unlock when it's actually
needed. Change the engine destruction order to avoid a race in the small
gap between pgraph and pfifo context uninitialization.

Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nv40_graph.c b/drivers/gpu/drm/nouveau/nv40_graph.c
index e0b41a26447..70d97cde49d 100644
--- a/drivers/gpu/drm/nouveau/nv40_graph.c
+++ b/drivers/gpu/drm/nouveau/nv40_graph.c
@@ -79,6 +79,22 @@ nv40_graph_create_context(struct nouveau_channel *chan)
 void
 nv40_graph_destroy_context(struct nouveau_channel *chan)
 {
+        struct drm_device *dev = chan->dev;
+        struct drm_nouveau_private *dev_priv = dev->dev_private;
+        struct nouveau_pgraph_engine *pgraph = &dev_priv->engine.graph;
+        unsigned long flags;
+
+        spin_lock_irqsave(&dev_priv->context_switch_lock, flags);
+        pgraph->fifo_access(dev, false);
+
+        /* Unload the context if it's the currently active one */
+        if (pgraph->channel(dev) == chan)
+                pgraph->unload_context(dev);
+
+        pgraph->fifo_access(dev, true);
+        spin_unlock_irqrestore(&dev_priv->context_switch_lock, flags);
+
+        /* Free the context resources */
         nouveau_gpuobj_ref(NULL, &chan->ramin_grctx);
 }