Hi, Chris,
On 1/22/20 4:56 PM, Chris Wilson wrote:
The file is not part of the global drm resource and can be released
prior to take the global mutex to drop the open_count (and potentially
close) the drm device.
However, inside drm_close_helper() there are a number of dev->driver
callbacks that take the drm_device as the first parameter... Worryingly
some of those callbacks may be (implicitly) depending on the global
mutex.
I read this as you suspect that there are driver callbacks inside
drm_close_helper() that might need the global mutex held? But then it
wouldn't be safe to move the lock? Is there a strong motivation for
moving the locking in the first place? Also a minor nit below:
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_file.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 92d16724f949..84ed313ee2e9 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -438,12 +438,12 @@ int drm_release(struct inode *inode, struct file *filp)
struct drm_minor *minor = file_priv->minor;
struct drm_device *dev = minor->dev;
- mutex_lock(&drm_global_mutex);
-
DRM_DEBUG("open_count = %d\n", dev->open_count);
The read of dev->open_count should still be inside the lock to be
consistent with the value that is decremented below. Perhaps move the
DRM_DEBUG()?
drm_close_helper(filp);
+ mutex_lock(&drm_global_mutex);
+
if (!--dev->open_count)
drm_lastclose(dev);
Thanks,
Thomas
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