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
thanks,
- Joel
