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>
diff --git a/drivers/char/drm/drm_lock.c b/drivers/char/drm/drm_lock.c
index b276ae8..b48a595 100644
--- a/drivers/char/drm/drm_lock.c
+++ b/drivers/char/drm/drm_lock.c
@@ -104,6 +104,10 @@
__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 @@
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 @@
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;
}
/**