Re: [PATCH v2 4/8] drm/msm/dpu: Disallow unallocated resources to be returned

[Dmitry Baryshkov]

On 09/01/2023 01:28, Dmitry Baryshkov wrote:
> On 22/12/2022 01:19, Marijn Suijten wrote:
> > In the event that the topology requests resources that have not been
> > created by the system (because they are typically not represented in
> > dpu_mdss_cfg ^1), the resource(s) in global_state (in this case DSC
> > blocks) remain NULL but will still be returned out of
> > dpu_rm_get_assigned_resources, where the caller expects to get an array
> > containing num_blks valid pointers (but instead gets these NULLs).
> >
> > To prevent this from happening, where null-pointer dereferences
> > typically result in a hard-to-debug platform lockup, num_blks shouldn't
> > increase past NULL blocks and will print an error and break instead.
> > After all, max_blks represents the static size of the maximum number of
> > blocks whereas the actual amount varies per platform.
> >
> > ^1: which can happen after a git rebase ended up moving additions to
> > _dpu_cfg to a different struct which has the same patch context.
> >
> > Fixes: bb00a452d6f7 ("drm/msm/dpu: Refactor resource manager")
> > Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 5 +++++
> >   1 file changed, 5 insertions(+)
>
> I think the patch is not fully correct. Please check resource 
> availability during allocation. I wouldn't expect an error from 
> get_assigned_resources because of resource exhaustion.

Another option, since allocation functions (except DSC) already have 
these safety checks: check error message to mention internal 
inconstency: allocated resource doesn't exist.

--
With best wishes
Dmitry