On Mon, Sep 28, 2026 at 5:20 AM Matthew Auld <[email protected]> wrote:
>
> On 25/09/2026 21:44, Bill Wendling wrote:
> > In 'struct gpu_buddy', the 'roots' field points to an array of pointers
> > to 'struct gpu_buddy_block'. The number of allocated roots is tracked
> > by the 'n_roots' field.
> >
> > Annotate the 'roots' pointer with the '__counted_by_ptr' attribute
> > referencing 'n_roots' to enable compile-time and runtime bounds-checking
> > via KASAN and '__builtin_dynamic_object_size'.
> >
> > In 'gpu_buddy_init', 'mm->n_roots' is initialized first, and 'mm->roots' is
> > subsequently allocated with 'kmalloc_objs(struct gpu_buddy_block *,
> > mm->n_roots)'.
> >
> > Since the bounds associated with 'roots' ('n_roots') are fully set prior
> > to any array allocation or access and remain invariant, this annotation
> > will not cause runtime panics or false-positive bounds checks.
> >
> > Cc: [email protected]
> > Assisted-by: LLM
> > Signed-off-by: Bill Wendling <[email protected]>
>
> Reviewed-by: Matthew Auld <[email protected]>
>
> Would it make sense to also do this for *_scoreboard and free_tree, if
> we add a new field n_orders?
>
Sure! There's already a 'max_order'. I assume that 'n_orders' would be
more dynamic?
-bw
> > ---
> > include/linux/gpu_buddy.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
> > index 2c36124bb696..d7249e500ab6 100644
> > --- a/include/linux/gpu_buddy.h
> > +++ b/include/linux/gpu_buddy.h
> > @@ -172,7 +172,7 @@ struct gpu_buddy {
> > * a power of two, with each root being the largest power-of-two
> > * that fits in the remaining space.
> > */
> > - struct gpu_buddy_block **roots;
> > + struct gpu_buddy_block **roots __counted_by_ptr(n_roots);
> > /*
> > * Per-order free block scoreboard: free_scoreboard[order] holds the
> > * number of blocks of that order currently in the free state.
>
