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, 1 insertions, 0 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_channel.c b/drivers/gpu/drm/nouveau/nouveau_channel.c
index 373950e34814..8636478c477a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_channel.c
+++ b/drivers/gpu/drm/nouveau/nouveau_channel.c
@@ -145,6 +145,7 @@ nouveau_channel_alloc(struct drm_device *dev, struct nouveau_channel **chan_ret,
 	chan->file_priv = file_priv;
 	chan->vram_handle = vram_handle;
 	chan->gart_handle = tt_handle;
+	mutex_init(&chan->mutex);
 
 	NV_INFO(dev, "Allocating FIFO number %d\n", channel);