Re: [PATCH drm-next v6 02/13] drm: manager to keep track of GPUs VA mappings

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 7 Jul 2023 14:41:23 +0200
Danilo Krummrich <dakr@redhat.com> wrote:

> >> +	     va__ && (va__->va.addr < (end__)) && \
> >> +	     !list_entry_is_head(va__, &(mgr__)->rb.list, rb.entry); \
> >> +	     va__ = list_next_entry(va__, rb.entry))  
> > 
> > If you define:
> > 
> > static inline struct drm_gpuva *
> > drm_gpuva_next(struct drm_gpuva *va)
> > {
> > 	if (va && !list_is_last(&va->rb.entry, &va->mgr->rb.list))
> > 		return list_next_entry(va, rb.entry);
> > 
> > 	return NULL;
> > } >
> > the for loop becomes a bit more readable:  
> 
> Yes, it would. However, I don't want it to be confused with 
> drm_gpuva_find_next(). Maybe I should rename the latter to something 
> like drm_gpuva_find_next_neighbor() then.

If you want to keep drm_gpuva_find_next(), feel free to rename/prefix
the drm_gpuva_next() function. I was just posting it as a reference.

> 
> > 
> > 	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__) - (start__)); \
> > 	     va__ && (va__->va.addr < (end__)); \
> > 	     va__ = drm_gpuva_next(va__))
> >   
> >> +
> >> +/**
> >> + * drm_gpuva_for_each_va_range_safe - iternator to safely walk over a range of
> >> + * &drm_gpuvas
> >> + * @va__: &drm_gpuva to assign to in each iteration step
> >> + * @next__: another &drm_gpuva to use as temporary storage
> >> + * @mgr__: &drm_gpuva_manager to walk over
> >> + * @start__: starting offset, the first gpuva will overlap this
> >> + * @end__: ending offset, the last gpuva will start before this (but may
> >> + * overlap)
> >> + *
> >> + * This iterator walks over all &drm_gpuvas in the &drm_gpuva_manager that lie
> >> + * between @start__ and @end__. It is implemented similarly to
> >> + * list_for_each_safe(), but is using the &drm_gpuva_manager's internal interval
> >> + * tree to accelerate the search for the starting &drm_gpuva, and hence is safe
> >> + * against removal of elements. It assumes that @end__ is within (or is the
> >> + * upper limit of) the &drm_gpuva_manager. This iterator does not skip over the
> >> + * &drm_gpuva_manager's @kernel_alloc_node.
> >> + */
> >> +#define drm_gpuva_for_each_va_range_safe(va__, next__, mgr__, start__, end__) \
> >> +	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__)), \
> >> +	     next__ = va ? list_next_entry(va__, rb.entry) : NULL; \
> >> +	     va__ && (va__->va.addr < (end__)) && \
> >> +	     !list_entry_is_head(va__, &(mgr__)->rb.list, rb.entry); \
> >> +	     va__ = next__, next__ = list_next_entry(va__, rb.entry))  
> > 
> > And this is the safe version using the drm_gpuva_next() helper:
> > 
> > 	for (va__ = drm_gpuva_find_first((mgr__), (start__), (end__) - (start__)), \
> > 	     next__ = drm_gpuva_next(va__); \
> > 	     va__ && (va__->va.addr < (end__)); \
> > 	     va__ = next__, next__ = drm_gpuva_next(va__))
> > 
> > Those changes fixed an invalid pointer access I had in the sm_unmap()
> > path.
> >   
> 
> Sorry you did run into this bug.

No worries, that's what testing/debugging/reviewing is for. And I'm glad
someone decided to work on this gpuva stuff so I don't have to code it
myself, so that's the least I can do.