Commit 7e13ad89 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm: Avoid drm_global_mutex for simple inc/dec of dev->open_count 



Since drm_global_mutex is a true global mutex across devices, we don't
want to acquire it unless absolutely necessary. For maintaining the
device local open_count, we can use atomic operations on the counter
itself, except when making the transition to/from 0. Here, we tackle the
easy portion of delaying acquiring the drm_global_mutex for the final
release by using atomic_dec_and_mutex_lock(), leaving the global
serialisation across the device opens.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Thomas Hellström (VMware) <thomas_os@shipmail.org>
Reviewed-by: default avatarThomas Hellström <thellstrom@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200124130107.125404-1-chris@chris-wilson.co.uk
parent 7a2c65dd

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

+1 −1
Original line number Diff line number Diff line
@@ -1137,7 +1137,7 @@ static bool amdgpu_switcheroo_can_switch(struct pci_dev *pdev) 
	* locking inversion with the driver load path. And the access here is

	* completely racy anyway. So don't bother with locking for now.

	*/

	return dev->open_count == 0;

	return atomic_read(&dev->open_count) == 0;

}



static const struct vga_switcheroo_client_ops amdgpu_switcheroo_ops = {

drivers/gpu/drm/drm_file.c

+8 −8
Original line number Diff line number Diff line
@@ -220,7 +220,7 @@ void drm_file_free(struct drm_file *file) 
	DRM_DEBUG("pid = %d, device = 0x%lx, open_count = %d\n",

		  task_pid_nr(current),

		  (long)old_encode_dev(file->minor->kdev->devt),

		  READ_ONCE(dev->open_count));

		  atomic_read(&dev->open_count));



	if (drm_core_check_feature(dev, DRIVER_LEGACY) &&

	    dev->driver->preclose)
@@ -379,7 +379,7 @@ int drm_open(struct inode *inode, struct file *filp) 
		return PTR_ERR(minor);



	dev = minor->dev;

	if (!dev->open_count++)

	if (!atomic_fetch_inc(&dev->open_count))

		need_setup = 1;



	/* share address_space across all char-devs of a single device */
@@ -398,7 +398,7 @@ int drm_open(struct inode *inode, struct file *filp) 
	return 0;



err_undo:

	dev->open_count--;

	atomic_dec(&dev->open_count);

	drm_minor_release(minor);

	return retcode;

}
@@ -440,11 +440,11 @@ int drm_release(struct inode *inode, struct file *filp) 


	mutex_lock(&drm_global_mutex);



	DRM_DEBUG("open_count = %d\n", dev->open_count);

	DRM_DEBUG("open_count = %d\n", atomic_read(&dev->open_count));



	drm_close_helper(filp);



	if (!--dev->open_count)

	if (atomic_dec_and_test(&dev->open_count))

		drm_lastclose(dev);



	mutex_unlock(&drm_global_mutex);
@@ -478,10 +478,10 @@ int drm_release_noglobal(struct inode *inode, struct file *filp) 


	drm_close_helper(filp);



	mutex_lock(&drm_global_mutex);

	if (!--dev->open_count)

	if (atomic_dec_and_mutex_lock(&dev->open_count, &drm_global_mutex)) {

		drm_lastclose(dev);

		mutex_unlock(&drm_global_mutex);

	}



	drm_minor_release(minor);

drivers/gpu/drm/i915/i915_switcheroo.c

+1 −1
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ static bool i915_switcheroo_can_switch(struct pci_dev *pdev) 
	 * locking inversion with the driver load path. And the access here is

	 * completely racy anyway. So don't bother with locking for now.

	 */

	return i915 && i915->drm.open_count == 0;

	return i915 && atomic_read(&i915->drm.open_count) == 0;

}



static const struct vga_switcheroo_client_ops i915_switcheroo_ops = {

drivers/gpu/drm/nouveau/nouveau_vga.c

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ nouveau_switcheroo_can_switch(struct pci_dev *pdev) 
	 * locking inversion with the driver load path. And the access here is

	 * completely racy anyway. So don't bother with locking for now.

	 */

	return dev->open_count == 0;

	return atomic_read(&dev->open_count) == 0;

}



static const struct vga_switcheroo_client_ops

drivers/gpu/drm/radeon/radeon_device.c

+1 −1
Original line number Diff line number Diff line
@@ -1263,7 +1263,7 @@ static bool radeon_switcheroo_can_switch(struct pci_dev *pdev) 
	 * locking inversion with the driver load path. And the access here is

	 * completely racy anyway. So don't bother with locking for now.

	 */

	return dev->open_count == 0;

	return atomic_read(&dev->open_count) == 0;

}



static const struct vga_switcheroo_client_ops radeon_switcheroo_ops = {

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