Re: Coverity: find_idlest_group(): Null pointer dereferences

[Vincent Guittot <vincent.guittot@linaro.org>]

On Tue, 29 Oct 2019 at 00:03, coverity-bot <keescook@chromium.org> wrote:
>
> Hello!
>
> This is an experimental automated report about issues detected by Coverity
> from a scan of next-20191025 as part of the linux-next weekly scan project:
> https://scan.coverity.com/projects/linux-next-weekly-scan
>
> You're getting this email because you were associated with the identified
> lines of code (noted below) that were touched by recent commits:
>
> 57abff067a08 ("sched/fair: Rework find_idlest_group()")
>
> Coverity reported the following:
>
> *** CID 1487371:  Null pointer dereferences  (FORWARD_NULL)
> /kernel/sched/fair.c: 8319 in find_idlest_group()
> 8313            case group_asym_packing:
> 8314                    /* Those type are not used in the slow wakeup path */
> 8315                    return NULL;
> 8316
> 8317            case group_misfit_task:
> 8318                    /* Select group with the highest max capacity */
> vvv     CID 1487371:  Null pointer dereferences  (FORWARD_NULL)
> vvv     Dereferencing null pointer "local".
> 8319                    if (local->sgc->max_capacity >= idlest->sgc->max_capacity)

Local can't be NULL and will be set in the loop above because this_cpu
belongs to one of the groups of its sched_domain

> 8320                            return NULL;
> 8321                    break;
> 8322
> 8323            case group_has_spare:
> 8324                    if (sd->flags & SD_NUMA) {
>
> If this is a false positive, please let us know so we can mark it as
> such, or teach the Coverity rules to be smarter. If not, please make
> sure fixes get into linux-next. :) For patches fixing this, please
> include:
>
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1487371 ("Null pointer dereferences")
> Fixes: 57abff067a08 ("sched/fair: Rework find_idlest_group()")
>
>
> Thanks for your attention!
>
> --
> Coverity-bot