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authorChris Wilson <chris@chris-wilson.co.uk>2020-01-24 13:01:07 +0000
committerChris Wilson <chris@chris-wilson.co.uk>2020-01-24 17:41:34 +0000
commit7e13ad896484a0165a68197a2e64091ea28c9602 (patch)
treea20b339f718dd71ca66899a60a970230acc5963a /drivers/gpu/drm/drm_file.c
parent7a2c65dd32b1cfa8bae55250dfdfe3d049e2f336 (diff)
downloadlinux-7e13ad896484a0165a68197a2e64091ea28c9602.tar.gz
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: Chris Wilson <chris@chris-wilson.co.uk> Cc: Thomas Hellström (VMware) <thomas_os@shipmail.org> Reviewed-by: Thomas Hellström <thellstrom@vmware.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200124130107.125404-1-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/gpu/drm/drm_file.c')
-rw-r--r--drivers/gpu/drm/drm_file.c16
1 files changed, 8 insertions, 8 deletions
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);