drm/nouveau: add per-channel mutex, use to lock access to drm's channel

This fixes a race condition between fbcon acceleration and TTM buffer
moves.  To reproduce:

- start X
- switch to vt and "while (true); do dmesg; done"
- switch to another vt and "sleep 2 && cat /path/to/debugfs/dri/0/evict_vram"
- switch back to vt running dmesg

We don't make use of this on any other channel yet, they're currently
protected by drm_global_mutex.  This will change in the near future.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
index 1c7db64c03bf..04bc56cf4f1a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drv.h
+++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
@@ -166,6 +166,8 @@ struct nouveau_channel {
         struct drm_device *dev;
         int id;
 
+        struct mutex mutex;
+
         /* owner of this fifo */
         struct drm_file *file_priv;
         /* mapping of the fifo itself */