[PATCH 1/2] dma-fence: export dma_fence_might_wait

[PATCH 1/2] dma-fence: export dma_fence_might_wait

[Matthew Auld]

It might be useful for drivers to annotate a path where hitting the
actual wait path might be difficult or unlikely through normal testing.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/dma-buf/dma-fence.c | 19 ++++++++++++++++---
 include/linux/dma-fence.h   |  2 ++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index ce0f5eff575d..f2cd036b5243 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -335,6 +335,21 @@ void __dma_fence_might_wait(void)
 }
 #endif
 
+/**
+ * dma_fence_might_wait - entering a section which might wait on DMA fence
+ * critical section.
+ *
+ * This is also potentially useful for drivers to call directly, when annotating
+ * a path where hitting the actual wait path might be difficult or unlikely
+ * through normal testing.
+ */
+void dma_fence_might_wait(void)
+{
+	might_sleep();
+	__dma_fence_might_wait();
+}
+EXPORT_SYMBOL(dma_fence_might_wait);
+
 
 /**
  * dma_fence_signal_timestamp_locked - signal completion of a fence
@@ -495,9 +510,7 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
 	if (WARN_ON(timeout < 0))
 		return -EINVAL;
 
-	might_sleep();
-
-	__dma_fence_might_wait();
+	dma_fence_might_wait();
 
 	trace_dma_fence_wait_start(fence);
 	if (fence->ops->wait)
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 6ffb4b2c6371..37bf4beed93f 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -370,6 +370,8 @@ static inline void dma_fence_end_signalling(bool cookie) {}
 static inline void __dma_fence_might_wait(void) {}
 #endif
 
+void dma_fence_might_wait(void);
+
 int dma_fence_signal(struct dma_fence *fence);
 int dma_fence_signal_locked(struct dma_fence *fence);
 int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
-- 
2.26.3

[PATCH 2/2] drm/i915: prefer dma_fence_might_wait in wait_migration

[Matthew Auld]

dma_fence_might_wait is more interesting here, since it also teaches
lockdep about the fence critical section and wait_migration dependency.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_wait.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
index f909aaa09d9c..190e221eaf81 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
@@ -305,7 +305,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,
 				   unsigned int flags)
 {
-	might_sleep();
+	dma_fence_might_wait();
 	/* NOP for now. */
 	return 0;
 }
-- 
2.26.3

Re: [PATCH 1/2] dma-fence: export dma_fence_might_wait

[Daniel Vetter]

On Tue, Jul 06, 2021 at 10:05:58AM +0100, Matthew Auld wrote:
> It might be useful for drivers to annotate a path where hitting the
> actual wait path might be difficult or unlikely through normal testing.
> 
> Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/dma-buf/dma-fence.c | 19 ++++++++++++++++---
>  include/linux/dma-fence.h   |  2 ++
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index ce0f5eff575d..f2cd036b5243 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -335,6 +335,21 @@ void __dma_fence_might_wait(void)
>  }
>  #endif
>  
> +/**
> + * dma_fence_might_wait - entering a section which might wait on DMA fence
> + * critical section.
> + *
> + * This is also potentially useful for drivers to call directly, when annotating
> + * a path where hitting the actual wait path might be difficult or unlikely
> + * through normal testing.

Maybe also add a

"See also dma_fence_begin_signalling() and dma_fence_end_signalling."

here and a similar note the these two functions pointing at
dma_fence_might_wait()? I do like to link things together when there's a
group of functions.

With that: Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> + */
> +void dma_fence_might_wait(void)
> +{
> +	might_sleep();
> +	__dma_fence_might_wait();
> +}
> +EXPORT_SYMBOL(dma_fence_might_wait);
> +
>  
>  /**
>   * dma_fence_signal_timestamp_locked - signal completion of a fence
> @@ -495,9 +510,7 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
>  	if (WARN_ON(timeout < 0))
>  		return -EINVAL;
>  
> -	might_sleep();
> -
> -	__dma_fence_might_wait();
> +	dma_fence_might_wait();
>  
>  	trace_dma_fence_wait_start(fence);
>  	if (fence->ops->wait)
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 6ffb4b2c6371..37bf4beed93f 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -370,6 +370,8 @@ static inline void dma_fence_end_signalling(bool cookie) {}
>  static inline void __dma_fence_might_wait(void) {}
>  #endif
>  
> +void dma_fence_might_wait(void);
> +
>  int dma_fence_signal(struct dma_fence *fence);
>  int dma_fence_signal_locked(struct dma_fence *fence);
>  int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
> -- 
> 2.26.3
> 

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

Re: [PATCH 2/2] drm/i915: prefer dma_fence_might_wait in wait_migration

[Daniel Vetter]

On Tue, Jul 06, 2021 at 10:05:59AM +0100, Matthew Auld wrote:
> dma_fence_might_wait is more interesting here, since it also teaches
> lockdep about the fence critical section and wait_migration dependency.
> 
> Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Ofc assuming nothing goes boom with lockdep :-)
-Daniel

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_wait.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> index f909aaa09d9c..190e221eaf81 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> @@ -305,7 +305,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,
>  				   unsigned int flags)
>  {
> -	might_sleep();
> +	dma_fence_might_wait();
>  	/* NOP for now. */
>  	return 0;
>  }
> -- 
> 2.26.3
> 

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

Re: [PATCH 1/2] dma-fence: export dma_fence_might_wait

[Daniel Vetter]

On Tue, Jul 06, 2021 at 11:14:01AM +0200, Daniel Vetter wrote:
> On Tue, Jul 06, 2021 at 10:05:58AM +0100, Matthew Auld wrote:
> > It might be useful for drivers to annotate a path where hitting the
> > actual wait path might be difficult or unlikely through normal testing.
> > 
> > Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/dma-buf/dma-fence.c | 19 ++++++++++++++++---
> >  include/linux/dma-fence.h   |  2 ++
> >  2 files changed, 18 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> > index ce0f5eff575d..f2cd036b5243 100644
> > --- a/drivers/dma-buf/dma-fence.c
> > +++ b/drivers/dma-buf/dma-fence.c
> > @@ -335,6 +335,21 @@ void __dma_fence_might_wait(void)
> >  }
> >  #endif
> >  
> > +/**
> > + * dma_fence_might_wait - entering a section which might wait on DMA fence
> > + * critical section.
> > + *
> > + * This is also potentially useful for drivers to call directly, when annotating
> > + * a path where hitting the actual wait path might be difficult or unlikely
> > + * through normal testing.
> 
> Maybe also add a
> 
> "See also dma_fence_begin_signalling() and dma_fence_end_signalling."
> 
> here and a similar note the these two functions pointing at
> dma_fence_might_wait()? I do like to link things together when there's a
> group of functions.
> 
> With that: Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Also ack for merging through drm-intel-gt-next, I don't think anything in
drm-misc plans to use this anytime soon. But please add the dma-buf Cc:
lines for the next round (dim add-missing-cc should cover you).
-Daniel

> 
> > + */
> > +void dma_fence_might_wait(void)
> > +{
> > +	might_sleep();
> > +	__dma_fence_might_wait();
> > +}
> > +EXPORT_SYMBOL(dma_fence_might_wait);
> > +
> >  
> >  /**
> >   * dma_fence_signal_timestamp_locked - signal completion of a fence
> > @@ -495,9 +510,7 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
> >  	if (WARN_ON(timeout < 0))
> >  		return -EINVAL;
> >  
> > -	might_sleep();
> > -
> > -	__dma_fence_might_wait();
> > +	dma_fence_might_wait();
> >  
> >  	trace_dma_fence_wait_start(fence);
> >  	if (fence->ops->wait)
> > diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> > index 6ffb4b2c6371..37bf4beed93f 100644
> > --- a/include/linux/dma-fence.h
> > +++ b/include/linux/dma-fence.h
> > @@ -370,6 +370,8 @@ static inline void dma_fence_end_signalling(bool cookie) {}
> >  static inline void __dma_fence_might_wait(void) {}
> >  #endif
> >  
> > +void dma_fence_might_wait(void);
> > +
> >  int dma_fence_signal(struct dma_fence *fence);
> >  int dma_fence_signal_locked(struct dma_fence *fence);
> >  int dma_fence_signal_timestamp(struct dma_fence *fence, ktime_t timestamp);
> > -- 
> > 2.26.3
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

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