drm/nouveau: Avoid potential race between nouveau_fence_update() and context takedown.

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index 01290d2952a..374a9793b85 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -77,14 +77,17 @@ nouveau_fence_update(struct nouveau_channel *chan)
 
         spin_lock(&chan->fence.lock);
 
-        if (USE_REFCNT(dev))
-                sequence = nvchan_rd32(chan, 0x48);
-        else
-                sequence = atomic_read(&chan->fence.last_sequence_irq);
-
-        if (chan->fence.sequence_ack == sequence)
-                goto out;
-        chan->fence.sequence_ack = sequence;
+        /* Fetch the last sequence if the channel is still up and running */
+        if (likely(!list_empty(&chan->fence.pending))) {
+                if (USE_REFCNT(dev))
+                        sequence = nvchan_rd32(chan, 0x48);
+                else
+                        sequence = atomic_read(&chan->fence.last_sequence_irq);
+
+                if (chan->fence.sequence_ack == sequence)
+                        goto out;
+                chan->fence.sequence_ack = sequence;
+        }
 
         list_for_each_entry_safe(fence, tmp, &chan->fence.pending, entry) {
                 sequence = fence->sequence;