| Message ID | 20200122155637.496291-1-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm: Release filp before global lock | expand |
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@chris-wilson.co.uk> > --- > 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
Quoting Thomas Hellström (VMware) (2020-01-22 21:52:23) > 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: The number of processes stuck on 'D' due to mutex_lock(&global) caught my attention while they were cleaning up files. I think everyone else will be less impressed if their driver was stuck because i915 was freeing a user's filp. > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > > --- > > 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()? Sure. Is it even worth a debug? -Chris
On 1/22/20 11:00 PM, Chris Wilson wrote: > Quoting Thomas Hellström (VMware) (2020-01-22 21:52:23) >> 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: > The number of processes stuck on 'D' due to mutex_lock(&global) caught my > attention while they were cleaning up files. I think everyone else will > be less impressed if their driver was stuck because i915 was freeing a > user's filp. Understood. Perhaps a short motivation in the log message? >>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> >>> --- >>> 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()? > Sure. Is it even worth a debug? Probably an old relic. I'm fine with letting it go. Thanks, Thomas > -Chris
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); drm_close_helper(filp); + mutex_lock(&drm_global_mutex); + if (!--dev->open_count) drm_lastclose(dev);
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. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> --- drivers/gpu/drm/drm_file.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)