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

[Abel Wu <wuyun.abel@bytedance.com>]

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@bytedance.com> 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@unisoc.com>
>>> ---
>>>    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;