drm/nouveau: protect ramht_find() from oopsing if on channel without ramht

This doesn't actually happen now, but there's a test case for an earlier
kernel where a GPU error is signalled on one of nv50's fake channels, and
the ramht lookup by the IRQ handler triggered an oops.

This adds a check for RAMHT's existance on a channel before looking up
an object handle.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_ramht.c b/drivers/gpu/drm/nouveau/nouveau_ramht.c
index de34b6bb059f..f240ba241943 100644
--- a/drivers/gpu/drm/nouveau/nouveau_ramht.c
+++ b/drivers/gpu/drm/nouveau/nouveau_ramht.c
@@ -197,6 +197,9 @@ nouveau_ramht_find(struct nouveau_channel *chan, u32 handle)
         struct nouveau_gpuobj *gpuobj = NULL;
         unsigned long flags;
 
+        if (unlikely(!chan->ramht))
+                return NULL;
+
         spin_lock_irqsave(&ramht->lock, flags);
         list_for_each_entry(entry, &chan->ramht->entries, head) {
                 if (entry->channel == chan && entry->handle == handle) {