drm: kill BKL from common code

This restricts the use of the big kernel lock to the i830 and i810
device drivers. The three remaining users in common code (open, ioctl
and release) get converted to a new mutex, the drm_global_mutex,
making the locking stricter than the big kernel lock.

This may have a performance impact, but only in those cases that
currently don't use DRM_UNLOCKED flag in the ioctl list and would
benefit from that anyway.

The reason why i810 and i830 cannot use drm_global_mutex in their
mmap functions is a lock-order inversion problem between the current
use of the BKL and mmap_sem in these drivers. Since the BKL has
release-on-sleep semantics, it's harmless but it would cause trouble
if we replace the BKL with a mutex.

Instead, these drivers get their own ioctl wrappers that take the
BKL around every ioctl call and then set their own handlers as
DRM_UNLOCKED.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

3 files changed, 30 insertions, 15 deletions

diff --git a/drivers/gpu/drm/i830/i830_dma.c b/drivers/gpu/drm/i830/i830_dma.c
index 7ee85ea507ce..5168862c9227 100644
--- a/drivers/gpu/drm/i830/i830_dma.c
+++ b/drivers/gpu/drm/i830/i830_dma.c
@@ -36,6 +36,7 @@
 #include "i830_drm.h"
 #include "i830_drv.h"
 #include <linux/interrupt.h>    /* For task queue support */
+#include <linux/smp_lock.h>
 #include <linux/pagemap.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
@@ -1509,21 +1510,34 @@ int i830_driver_dma_quiescent(struct drm_device *dev)
         return 0;
 }
 
+/*
+ * call the drm_ioctl under the big kernel lock because
+ * to lock against the i830_mmap_buffers function.
+ */
+long i830_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+        int ret;
+        lock_kernel();
+        ret = drm_ioctl(file, cmd, arg);
+        unlock_kernel();
+        return ret;
+}
+
 struct drm_ioctl_desc i830_ioctls[] = {
-        DRM_IOCTL_DEF(DRM_I830_INIT, i830_dma_init, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),
-        DRM_IOCTL_DEF(DRM_I830_VERTEX, i830_dma_vertex, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_CLEAR, i830_clear_bufs, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_FLUSH, i830_flush_ioctl, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_GETAGE, i830_getage, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_GETBUF, i830_getbuf, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_SWAP, i830_swap_bufs, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_COPY, i830_copybuf, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_DOCOPY, i830_docopy, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_FLIP, i830_flip_bufs, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_IRQ_EMIT, i830_irq_emit, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_IRQ_WAIT, i830_irq_wait, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_GETPARAM, i830_getparam, DRM_AUTH),
-        DRM_IOCTL_DEF(DRM_I830_SETPARAM, i830_setparam, DRM_AUTH)
+        DRM_IOCTL_DEF(DRM_I830_INIT, i830_dma_init, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_VERTEX, i830_dma_vertex, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_CLEAR, i830_clear_bufs, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_FLUSH, i830_flush_ioctl, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_GETAGE, i830_getage, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_GETBUF, i830_getbuf, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_SWAP, i830_swap_bufs, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_COPY, i830_copybuf, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_DOCOPY, i830_docopy, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_FLIP, i830_flip_bufs, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_IRQ_EMIT, i830_irq_emit, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_IRQ_WAIT, i830_irq_wait, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_GETPARAM, i830_getparam, DRM_AUTH|DRM_UNLOCKED),
+        DRM_IOCTL_DEF(DRM_I830_SETPARAM, i830_setparam, DRM_AUTH|DRM_UNLOCKED),
 };
 
 int i830_max_ioctl = DRM_ARRAY_SIZE(i830_ioctls);
diff --git a/drivers/gpu/drm/i830/i830_drv.c b/drivers/gpu/drm/i830/i830_drv.c
index 44f990bed8f4..a5c66aa82f0c 100644
--- a/drivers/gpu/drm/i830/i830_drv.c
+++ b/drivers/gpu/drm/i830/i830_drv.c
@@ -70,7 +70,7 @@ static struct drm_driver driver = {
                  .owner = THIS_MODULE,
                  .open = drm_open,
                  .release = drm_release,
-                 .unlocked_ioctl = drm_ioctl,
+                 .unlocked_ioctl = i830_ioctl,
                  .mmap = drm_mmap,
                  .poll = drm_poll,
                  .fasync = drm_fasync,
diff --git a/drivers/gpu/drm/i830/i830_drv.h b/drivers/gpu/drm/i830/i830_drv.h
index ecfd25a35da3..0df1c720560b 100644
--- a/drivers/gpu/drm/i830/i830_drv.h
+++ b/drivers/gpu/drm/i830/i830_drv.h
@@ -122,6 +122,7 @@ typedef struct drm_i830_private {
 
 } drm_i830_private_t;
 
+long i830_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 extern struct drm_ioctl_desc i830_ioctls[];
 extern int i830_max_ioctl;