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 chris@chris-wilson.co.uk Cc: Thomas Hellström (VMware) thomas_os@shipmail.org --- drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 2 +- drivers/gpu/drm/drm_file.c | 14 ++++++-------- 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, 11 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..c4e9ef86c589 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 +478,8 @@ 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);
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;