Re: Re: [PATCH] sched/eevdf: Avoid NULL in pick_eevdf

[Abel Wu]

On 12/12/23 10:51 AM, Xuewen Yan Wrote:
> Hi Abel
>
> On Mon, Nov 20, 2023 at 4:49 PM Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote:
> > Hi Xuewen, the pick part has been re-worked, would you please re-test
> > with the newest branch?
> >
> > Thanks,
> >          Abel
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/?h=sched%2Fcore
>
> These patches would be merged into 6.6? If not, the pr_err also has a deadlock.
> And should be changed to printk_deferred.

Yes, they will be merged in Linus's tree.

> 954 static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
>    955 {
>    956         struct sched_entity *se = __pick_eevdf(cfs_rq);
>    957
>    958         if (!se) {
>    959                 struct sched_entity *left = __pick_first_entity(cfs_rq);
>    960                 if (left) {
>    961                         pr_err("EEVDF scheduling fail, picking
> leftmost\n"); <<<<
>    962                         return left;
>    963                 }
>    964         }
>    965
>    966         return se;
>    967 }
>
>
> > On 11/20/23 3:38 PM, Xuewen Yan Wrote:
> > > Now in pick_eevdf function, add the pick_first_entity to prevent
> > > picking null when using eevdf, however, the leftmost may be null.
> > > As a result, it would cause oops because the se is NULL.
> > >
> > > Fix this by compare the curr and left, if the left is null, set
> > > the se be curr.
> > >
> > > Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy")
> > > Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
> > > ---
> > >    kernel/sched/fair.c | 18 +++++++++++++++++-
> > >    1 file changed, 17 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index d7a3c63a2171..10916f6778ac 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -951,12 +951,28 @@ static struct sched_entity *__pick_eevdf(struct cfs_rq *cfs_rq)
> > >        return NULL;
> > >    }
> > >
> > > +/* Just simply choose the se with the smallest vruntime */
> > > +static struct sched_entity *__pick_cfs(struct cfs_rq *cfs_rq)
> > > +{
> > > +     struct sched_entity *curr = cfs_rq->curr;
> > > +     struct sched_entity *left = __pick_first_entity(cfs_rq);
> > > +
> > > +     /*
> > > +      * If curr is set we have to see if its left of the leftmost entity
> > > +      * still in the tree, provided there was anything in the tree at all.
> > > +      */
> > > +     if (!left || (curr && entity_before(curr, left)))
> > > +             left = curr;
> > > +
> > > +     return left;
> > > +}
> > > +
> > >    static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
> > >    {
> > >        struct sched_entity *se = __pick_eevdf(cfs_rq);
> > >
> > >        if (!se) {
> > > -             struct sched_entity *left = __pick_first_entity(cfs_rq);
> > > +             struct sched_entity *left = __pick_cfs(cfs_rq);
> > >                if (left) {
> > >                        pr_err("EEVDF scheduling fail, picking leftmost\n");
> > >                        return left;