drm: fix quiescent locking

A fix for a locking bug which is triggered when a client tries to lock with
flag DMA_QUIESCENT (typically the X server), but gets interrupted by a signal.
The locking IOCTL should then return an error, but if DMA_QUIESCENT succeeds
it returns 0, and the client falsely thinks it has the lock. In addition
The client waits for DMA_QUISCENT and possibly DMA_READY without having the lock.

From: Thomas Hellstrom
Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/char/drm/drm_lock.c b/drivers/char/drm/drm_lock.c
index b276ae8a6633..b48a595d54ec 100644
--- a/drivers/char/drm/drm_lock.c
+++ b/drivers/char/drm/drm_lock.c
@@ -104,6 +104,10 @@ int drm_lock(struct inode *inode, struct file *filp,
         __set_current_state(TASK_RUNNING);
         remove_wait_queue(&dev->lock.lock_queue, &entry);
 
+        DRM_DEBUG("%d %s\n", lock.context, ret ? "interrupted" : "has lock");
+        if (ret)
+                return ret;
+
         sigemptyset(&dev->sigmask);
         sigaddset(&dev->sigmask, SIGSTOP);
         sigaddset(&dev->sigmask, SIGTSTP);
@@ -116,8 +120,12 @@ int drm_lock(struct inode *inode, struct file *filp,
         if (dev->driver->dma_ready && (lock.flags & _DRM_LOCK_READY))
                 dev->driver->dma_ready(dev);
 
-        if (dev->driver->dma_quiescent && (lock.flags & _DRM_LOCK_QUIESCENT))
-                return dev->driver->dma_quiescent(dev);
+        if (dev->driver->dma_quiescent && (lock.flags & _DRM_LOCK_QUIESCENT)) {
+                if (dev->driver->dma_quiescent(dev)) {
+                        DRM_DEBUG("%d waiting for DMA quiescent\n", lock.context);
+                        return DRM_ERR(EBUSY);
+                }
+        }
 
         /* dev->driver->kernel_context_switch isn't used by any of the x86
          *  drivers but is used by the Sparc driver.
@@ -128,9 +136,7 @@ int drm_lock(struct inode *inode, struct file *filp,
                 dev->driver->kernel_context_switch(dev, dev->last_context,
                                                    lock.context);
         }
-        DRM_DEBUG("%d %s\n", lock.context, ret ? "interrupted" : "has lock");
-
-        return ret;
+        return 0;
 }
 
 /**