Re: [Intel-gfx] [PATCH v8 3/7] drm: lock drm_global_mutex earlier in the ioctl handler

2021-08-30 Thread Desmond Cheong Zhi Xi 

On 26/8/21 5:58 pm, Daniel Vetter wrote:

On Thu, Aug 26, 2021 at 10:01:18AM +0800, Desmond Cheong Zhi Xi wrote:

In a future patch, a read lock on drm_device.master_rwsem is
held in the ioctl handler before the check for ioctl
permissions. However, this inverts the lock hierarchy of
drm_global_mutex --> master_rwsem.

To avoid this, we do some prep work to grab the drm_global_mutex
before checking for ioctl permissions.

Signed-off-by: Desmond Cheong Zhi Xi 
---
  drivers/gpu/drm/drm_ioctl.c | 18 +-
  1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index d25713b09b80..158629d88319 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -772,19 +772,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t 
*func, void *kdata,
if (drm_dev_is_unplugged(dev))
return -ENODEV;
  
+	/* Enforce sane locking for modern driver ioctls. */

+   if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
DRM_UNLOCKED))


Maybe have a local bool locked_ioctl for this so it's extremely clear it's
the same condition in both?

Either way: Reviewed-by: Daniel Vetter 



Thanks for the suggestion and review. Sounds good, I'll update and send 
out a new version.


(Sorry for delays, been busy with moving)


+   mutex_lock(_global_mutex);
+
retcode = drm_ioctl_permit(flags, file_priv);
if (unlikely(retcode))
-   return retcode;
+   goto out;
  
-	/* Enforce sane locking for modern driver ioctls. */

-   if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
-   (flags & DRM_UNLOCKED))
-   retcode = func(dev, kdata, file_priv);
-   else {
-   mutex_lock(_global_mutex);
-   retcode = func(dev, kdata, file_priv);
+   retcode = func(dev, kdata, file_priv);
+
+out:
+   if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
DRM_UNLOCKED))
mutex_unlock(_global_mutex);
-   }
return retcode;
  }
  EXPORT_SYMBOL(drm_ioctl_kernel);
--
2.25.1

Re: [Intel-gfx] [PATCH v8 3/7] drm: lock drm_global_mutex earlier in the ioctl handler

2021-08-26 Thread Daniel Vetter 
On Thu, Aug 26, 2021 at 10:01:18AM +0800, Desmond Cheong Zhi Xi wrote:
> In a future patch, a read lock on drm_device.master_rwsem is
> held in the ioctl handler before the check for ioctl
> permissions. However, this inverts the lock hierarchy of
> drm_global_mutex --> master_rwsem.
> 
> To avoid this, we do some prep work to grab the drm_global_mutex
> before checking for ioctl permissions.
> 
> Signed-off-by: Desmond Cheong Zhi Xi 
> ---
>  drivers/gpu/drm/drm_ioctl.c | 18 +-
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index d25713b09b80..158629d88319 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -772,19 +772,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t 
> *func, void *kdata,
>   if (drm_dev_is_unplugged(dev))
>   return -ENODEV;
>  
> + /* Enforce sane locking for modern driver ioctls. */
> + if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
> DRM_UNLOCKED))

Maybe have a local bool locked_ioctl for this so it's extremely clear it's
the same condition in both?

Either way: Reviewed-by: Daniel Vetter 

> + mutex_lock(_global_mutex);
> +
>   retcode = drm_ioctl_permit(flags, file_priv);
>   if (unlikely(retcode))
> - return retcode;
> + goto out;
>  
> - /* Enforce sane locking for modern driver ioctls. */
> - if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
> - (flags & DRM_UNLOCKED))
> - retcode = func(dev, kdata, file_priv);
> - else {
> - mutex_lock(_global_mutex);
> - retcode = func(dev, kdata, file_priv);
> + retcode = func(dev, kdata, file_priv);
> +
> +out:
> + if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
> DRM_UNLOCKED))
>   mutex_unlock(_global_mutex);
> - }
>   return retcode;
>  }
>  EXPORT_SYMBOL(drm_ioctl_kernel);
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

[Intel-gfx] [PATCH v8 3/7] drm: lock drm_global_mutex earlier in the ioctl handler

2021-08-25 Thread Desmond Cheong Zhi Xi 
In a future patch, a read lock on drm_device.master_rwsem is
held in the ioctl handler before the check for ioctl
permissions. However, this inverts the lock hierarchy of
drm_global_mutex --> master_rwsem.

To avoid this, we do some prep work to grab the drm_global_mutex
before checking for ioctl permissions.

Signed-off-by: Desmond Cheong Zhi Xi 
---
 drivers/gpu/drm/drm_ioctl.c | 18 +-
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index d25713b09b80..158629d88319 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -772,19 +772,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t 
*func, void *kdata,
if (drm_dev_is_unplugged(dev))
return -ENODEV;
 
+   /* Enforce sane locking for modern driver ioctls. */
+   if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
DRM_UNLOCKED))
+   mutex_lock(_global_mutex);
+
retcode = drm_ioctl_permit(flags, file_priv);
if (unlikely(retcode))
-   return retcode;
+   goto out;
 
-   /* Enforce sane locking for modern driver ioctls. */
-   if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) ||
-   (flags & DRM_UNLOCKED))
-   retcode = func(dev, kdata, file_priv);
-   else {
-   mutex_lock(_global_mutex);
-   retcode = func(dev, kdata, file_priv);
+   retcode = func(dev, kdata, file_priv);
+
+out:
+   if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && !(flags & 
DRM_UNLOCKED))
mutex_unlock(_global_mutex);
-   }
return retcode;
 }
 EXPORT_SYMBOL(drm_ioctl_kernel);
-- 
2.25.1