On Wed, 2023-03-01 at 18:25 +0100, Jakob Koschel wrote:
> If potentially no valid element is found, 'pstate' would contain an
> invalid pointer past the iterator loop. To ensure 'pstate' is always
> valid, we only set it if the correct element was found. That allows
> adding a BUG_ON in case the code works incorrectly, exposing currently
> undetectable potential bugs.
>
> Additionally, Linus proposed to avoid any use of the list iterator
> variable after the loop, in the attempt to move the list iterator
> variable declaration into the marcro to avoid any potential misuse after
> the loop [1].
>
> Link:
> https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=ehreask5sqxpwr9y7k9sa6cwx...@mail.gmail.com/
> [1]
> Signed-off-by: Jakob Koschel <[email protected]>
> ---
> drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c
> b/drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c
> index ce774579c89d..7c9dd91e98ee 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c
> @@ -72,7 +72,7 @@ nvkm_control_mthd_pstate_attr(struct nvkm_control *ctrl,
> void *data, u32 size)
> } *args = data;
> struct nvkm_clk *clk = ctrl->device->clk;
> const struct nvkm_domain *domain;
> - struct nvkm_pstate *pstate;
> + struct nvkm_pstate *pstate = NULL, *iter;
> struct nvkm_cstate *cstate;
> int i = 0, j = -1;
> u32 lo, hi;
> @@ -103,11 +103,14 @@ nvkm_control_mthd_pstate_attr(struct nvkm_control
> *ctrl, void *data, u32 size)
> return -EINVAL;
>
> if (args->v0.state != NVIF_CONTROL_PSTATE_ATTR_V0_STATE_CURRENT) {
> - list_for_each_entry(pstate, &clk->states, head) {
> - if (i++ == args->v0.state)
> + list_for_each_entry(iter, &clk->states, head) {
> + if (i++ == args->v0.state) {
> + pstate = iter;
> break;
> + }
> }
>
> + BUG_ON(!pstate);
Let's replace this with
if (WARN_ON_ONCE(!pstate))
return -EINVAL;
> lo = pstate->base.domain[domain->name];
> hi = lo;
> list_for_each_entry(cstate, &pstate->list, head) {
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
