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: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Thomas Hellström (VMware) <thomas...@shipmail.org>
---
atomic_dec_and_mutex_lock needs pairing with mutex_unlock (you fool)
---
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 2 +-
drivers/gpu/drm/drm_file.c | 16 ++++++++--------
drivers/gpu/drm/i915/i915_switcheroo.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_vga.c | 2 +-
drivers/gpu/drm/radeon/radeon_device.c | 2 +-
include/drm/drm_device.h | 2 +-
6 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 53d882000101..c3c0356dfa61 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1136,7 +1136,7 @@ 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 = {
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index e25306c49cc6..1075b3a8b5b1 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -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);
+ mutex_unlock(&drm_global_mutex);
+ }
drm_minor_release(minor);
diff --git a/drivers/gpu/drm/i915/i915_switcheroo.c
b/drivers/gpu/drm/i915/i915_switcheroo.c
index 39c79e1c5b52..ed69b5d4a375 100644
--- a/drivers/gpu/drm/i915/i915_switcheroo.c
+++ b/drivers/gpu/drm/i915/i915_switcheroo.c
@@ -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 = {
diff --git a/drivers/gpu/drm/nouveau/nouveau_vga.c
b/drivers/gpu/drm/nouveau/nouveau_vga.c
index d865d8aeac3c..c85dd8afa3c3 100644
--- a/drivers/gpu/drm/nouveau/nouveau_vga.c
+++ b/drivers/gpu/drm/nouveau/nouveau_vga.c
@@ -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
diff --git a/drivers/gpu/drm/radeon/radeon_device.c
b/drivers/gpu/drm/radeon/radeon_device.c
index a522e092038b..266e3cbbd09b 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -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 = {
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 1acfc3bbd3fb..bb60a949f416 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -144,7 +144,7 @@ struct drm_device {
* Usage counter for outstanding files open,
* protected by drm_global_mutex
*/
- int open_count;
+ atomic_t open_count;
/** @filelist_mutex: Protects @filelist. */
struct mutex filelist_mutex;
--
2.25.0
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
