Commit 58374713 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Dave Airlie
Browse files

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: default avatarArnd Bergmann <arnd@arndb.de>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent a1e09b62

drivers/gpu/drm/drm_drv.c

+2 −2
Original line number Diff line number Diff line
@@ -481,9 +481,9 @@ 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) {

drivers/gpu/drm/drm_fops.c

+11 −12
Original line number Diff line number Diff line
@@ -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;

}

drivers/gpu/drm/i810/i810_dma.c

+29 −15
Original line number Diff line number Diff line
@@ -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
@@ -1240,22 +1241,35 @@ 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);

drivers/gpu/drm/i810/i810_drv.c

+1 −1
Original line number Diff line number Diff line
@@ -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,

drivers/gpu/drm/i810/i810_drv.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

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