On 2020/10/24 5:47, Joel Fernandes wrote:
> On Fri, Oct 23, 2020 at 01:25:38PM +0800, Li, Aubrey wrote:
>>>>> @@ -2517,6 +2528,7 @@ const struct sched_class dl_sched_class
>>>>>
>>>>> #ifdef CONFIG_SMP
>>>>> .balance = balance_dl,
>>>>> + .pick_task = pick_task_dl,
>>>>> .select_task_rq = select_task_rq_dl,
>>>>> .migrate_task_rq = migrate_task_rq_dl,
>>>>> .set_cpus_allowed = set_cpus_allowed_dl,
>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>>> index dbd9368a959d..bd6aed63f5e3 100644
>>>>> --- a/kernel/sched/fair.c
>>>>> +++ b/kernel/sched/fair.c
>>>>> @@ -4450,7 +4450,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct
>>>>> sched_entity *curr)
>>>>> * Avoid running the skip buddy, if running something else can
>>>>> * be done without getting too unfair.
>>>>> */
>>>>> - if (cfs_rq->skip == se) {
>>>>> + if (cfs_rq->skip && cfs_rq->skip == se) {
>>>>> struct sched_entity *second;
>>>>>
>>>>> if (se == curr) {
>>>>> @@ -6976,6 +6976,35 @@ static void check_preempt_wakeup(struct rq *rq,
>>>>> struct task_struct *p, int wake_
>>>>> set_last_buddy(se);
>>>>> }
>>>>>
>>>>> +#ifdef CONFIG_SMP
>>>>> +static struct task_struct *pick_task_fair(struct rq *rq)
>>>>> +{
>>>>> + struct cfs_rq *cfs_rq = &rq->cfs;
>>>>> + struct sched_entity *se;
>>>>> +
>>>>> + if (!cfs_rq->nr_running)
>>>>> + return NULL;
>>>>> +
>>>>> + do {
>>>>> + struct sched_entity *curr = cfs_rq->curr;
>>>>> +
>>>>> + se = pick_next_entity(cfs_rq, NULL);
>>>>> +
>>>>> + if (curr) {
>>>>> + if (se && curr->on_rq)
>>>>> + update_curr(cfs_rq);
>>>>> +
>>>>> + if (!se || entity_before(curr, se))
>>>>> + se = curr;
>>>>> + }
>>>>> +
>>>>> + cfs_rq = group_cfs_rq(se);
>>>>> + } while (cfs_rq);
>>>>> ++
>>>>> + return task_of(se);
>>>>> +}
>>>>> +#endif
>>>>
>>>> One of my machines hangs when I run uperf with only one message:
>>>> [ 719.034962] BUG: kernel NULL pointer dereference, address:
>>>> 0000000000000050
>>>>
>>>> Then I replicated the problem on my another machine(no serial console),
>>>> here is the stack by manual copy.
>>>>
>>>> Call Trace:
>>>> pick_next_entity+0xb0/0x160
>>>> pick_task_fair+0x4b/0x90
>>>> __schedule+0x59b/0x12f0
>>>> schedule_idle+0x1e/0x40
>>>> do_idle+0x193/0x2d0
>>>> cpu_startup_entry+0x19/0x20
>>>> start_secondary+0x110/0x150
>>>> secondary_startup_64_no_verify+0xa6/0xab
>>>
>>> Interesting. Wondering if we screwed something up in the rebase.
>>>
>>> Questions:
>>> 1. Does the issue happen if you just apply only up until this patch,
>>> or the entire series?
>>
>> I applied the entire series and just find a related patch to report the
>> issue.
>
> Ok.
>
>>> 2. Do you see the issue in v7? Not much if at all has changed in this
>>> part of the code from v7 -> v8 but could be something in the newer
>>> kernel.
>>>
>>
>> IIRC, I can run uperf successfully on v7.
>> I'm on tip/master 2d3e8c9424c9 (origin/master) "Merge branch 'linus'."
>> Please let me know if this is a problem, or you have a repo I can pull
>> for testing.
>
> Here is a repo with v8 series on top of v5.9 release:
> https://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git/log/?h=coresched-v5.9
I didn't see NULL pointer dereference BUG of this repo, will post performance
data later.
Thanks,
-Aubrey
