[PATCH 1/3] drm: kill BKL from common code

[Arnd Bergmann <arnd@arndb.de>]

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
---
 drivers/gpu/drm/drm_drv.c       |    4 +-
 drivers/gpu/drm/drm_fops.c      |   23 +++++++++----------
 drivers/gpu/drm/i810/i810_dma.c |   44 +++++++++++++++++++++++++-------------
 drivers/gpu/drm/i810/i810_drv.c |    2 +-
 drivers/gpu/drm/i810/i810_drv.h |    1 +
 drivers/gpu/drm/i830/i830_dma.c |   42 ++++++++++++++++++++++++------------
 drivers/gpu/drm/i830/i830_drv.c |    2 +-
 drivers/gpu/drm/i830/i830_drv.h |    1 +
 include/drm/drmP.h              |    2 +-
 9 files changed, 75 insertions(+), 46 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 4a66201..76d98f4 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -506,9 +506,9 @@ long drm_ioctl(struct file *filp,
 		if (ioctl->flags & DRM_UNLOCKED)
 			retcode = func(dev, kdata, file_priv);
 		else {
-			lock_kernel();
+			mutex_lock(&drm_global_mutex);
 			retcode = func(dev, kdata, file_priv);
-			unlock_kernel();
+			mutex_unlock(&drm_global_mutex);
 		}
 
 		if (cmd & IOC_OUT) {
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index e7aace2..2ca8df8 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -39,6 +39,9 @@
 #include <linux/slab.h>
 #include <linux/smp_lock.h>
 
+/* from BKL pushdown: note that nothing else serializes idr_find() */
+DEFINE_MUTEX(drm_global_mutex);
+
 static int drm_open_helper(struct inode *inode, struct file *filp,
 			   struct drm_device * dev);
 
@@ -175,8 +178,7 @@ int drm_stub_open(struct inode *inode, struct file *filp)
 
 	DRM_DEBUG("\n");
 
-	/* BKL pushdown: note that nothing else serializes idr_find() */
-	lock_kernel();
+	mutex_lock(&drm_global_mutex);
 	minor = idr_find(&drm_minors_idr, minor_id);
 	if (!minor)
 		goto out;
@@ -197,7 +199,7 @@ int drm_stub_open(struct inode *inode, struct file *filp)
 	fops_put(old_fops);
 
 out:
-	unlock_kernel();
+	mutex_unlock(&drm_global_mutex);
 	return err;
 }
 
@@ -472,7 +474,7 @@ int drm_release(struct inode *inode, struct file *filp)
 	struct drm_device *dev = file_priv->minor->dev;
 	int retcode = 0;
 
-	lock_kernel();
+	mutex_lock(&drm_global_mutex);
 
 	DRM_DEBUG("open_count = %d\n", dev->open_count);
 
@@ -573,17 +575,14 @@ int drm_release(struct inode *inode, struct file *filp)
 		if (atomic_read(&dev->ioctl_count)) {
 			DRM_ERROR("Device busy: %d\n",
 				  atomic_read(&dev->ioctl_count));
-			spin_unlock(&dev->count_lock);
-			unlock_kernel();
-			return -EBUSY;
+			retcode = -EBUSY;
+			goto out;
 		}
-		spin_unlock(&dev->count_lock);
-		unlock_kernel();
-		return drm_lastclose(dev);
+		retcode = drm_lastclose(dev);
 	}
+out:
 	spin_unlock(&dev->count_lock);
-
-	unlock_kernel();
+	mutex_unlock(&drm_global_mutex);
 
 	return retcode;
 }
diff --git a/drivers/gpu/drm/i810/i810_dma.c b/drivers/gpu/drm/i810/i810_dma.c
index 997d917..0090693 100644
--- a/drivers/gpu/drm/i810/i810_dma.c
+++ b/drivers/gpu/drm/i810/i810_dma.c
@@ -37,6 +37,7 @@
 #include <linux/interrupt.h>	/* For task queue support */
 #include <linux/delay.h>
 #include <linux/slab.h>
+#include <linux/smp_lock.h>
 #include <linux/pagemap.h>
 
 #define I810_BUF_FREE		2
@@ -1245,22 +1246,35 @@ int i810_driver_dma_quiescent(struct drm_device * dev)
 	return 0;
 }
 
+/*
+ * call the drm_ioctl under the big kernel lock because
+ * to lock against the i810_mmap_buffers function.
+ */
+long i810_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 i810_ioctls[] = {
-	DRM_IOCTL_DEF(DRM_I810_INIT, i810_dma_init, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),
-	DRM_IOCTL_DEF(DRM_I810_VERTEX, i810_dma_vertex, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_CLEAR, i810_clear_bufs, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_FLUSH, i810_flush_ioctl, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_GETAGE, i810_getage, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_GETBUF, i810_getbuf, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_SWAP, i810_swap_bufs, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_COPY, i810_copybuf, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_DOCOPY, i810_docopy, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_OV0INFO, i810_ov0_info, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_FSTATUS, i810_fstatus, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_OV0FLIP, i810_ov0_flip, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_MC, i810_dma_mc, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),
-	DRM_IOCTL_DEF(DRM_I810_RSTATUS, i810_rstatus, DRM_AUTH),
-	DRM_IOCTL_DEF(DRM_I810_FLIP, i810_flip_bufs, DRM_AUTH)
+	DRM_IOCTL_DEF(DRM_I810_INIT, i810_dma_init, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_VERTEX, i810_dma_vertex, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_CLEAR, i810_clear_bufs, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_FLUSH, i810_flush_ioctl, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_GETAGE, i810_getage, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_GETBUF, i810_getbuf, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_SWAP, i810_swap_bufs, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_COPY, i810_copybuf, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_DOCOPY, i810_docopy, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_OV0INFO, i810_ov0_info, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_FSTATUS, i810_fstatus, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_OV0FLIP, i810_ov0_flip, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_MC, i810_dma_mc, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_RSTATUS, i810_rstatus, DRM_AUTH|DRM_UNLOCKED),
+	DRM_IOCTL_DEF(DRM_I810_FLIP, i810_flip_bufs, DRM_AUTH|DRM_UNLOCKED),
 };
 
 int i810_max_ioctl = DRM_ARRAY_SIZE(i810_ioctls);
diff --git a/drivers/gpu/drm/i810/i810_drv.c b/drivers/gpu/drm/i810/i810_drv.c
index c1e0275..b4250b2 100644
--- a/drivers/gpu/drm/i810/i810_drv.c
+++ b/drivers/gpu/drm/i810/i810_drv.c
@@ -59,7 +59,7 @@ static struct drm_driver driver = {
 		 .owner = THIS_MODULE,
 		 .open = drm_open,
 		 .release = drm_release,
-		 .unlocked_ioctl = drm_ioctl,
+		 .unlocked_ioctl = i810_ioctl,
 		 .mmap = drm_mmap,
 		 .poll = drm_poll,
 		 .fasync = drm_fasync,
diff --git a/drivers/gpu/drm/i810/i810_drv.h b/drivers/gpu/drm/i810/i810_drv.h
index 21e2691..cac8f37 100644
--- a/drivers/gpu/drm/i810/i810_drv.h
+++ b/drivers/gpu/drm/i810/i810_drv.h
@@ -126,6 +126,7 @@ extern void i810_driver_reclaim_buffers_locked(struct drm_device * dev,
 					       struct drm_file *file_priv);
 extern int i810_driver_device_is_agp(struct drm_device * dev);
 
+extern long i810_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 extern struct drm_ioctl_desc i810_ioctls[];
 extern int i810_max_ioctl;
 
diff --git a/drivers/gpu/drm/i830/i830_dma.c b/drivers/gpu/drm/i830/i830_dma.c
index 65759a9..7a31d71 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>
@@ -1516,21 +1517,34 @@ 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 44f990b..a5c66aa 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 da82afe..d8df717 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;
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index c1b9871..cd0e56b 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -50,7 +50,6 @@
 #include <linux/file.h>
 #include <linux/pci.h>
 #include <linux/jiffies.h>
-#include <linux/smp_lock.h>	/* For (un)lock_kernel */
 #include <linux/dma-mapping.h>
 #include <linux/mm.h>
 #include <linux/cdev.h>
@@ -1138,6 +1137,7 @@ extern long drm_compat_ioctl(struct file *filp,
 extern int drm_lastclose(struct drm_device *dev);
 
 				/* Device support (drm_fops.h) */
+extern struct mutex drm_global_mutex;
 extern int drm_open(struct inode *inode, struct file *filp);
 extern int drm_stub_open(struct inode *inode, struct file *filp);
 extern int drm_fasync(int fd, struct file *filp, int on);
-- 
1.7.1