On 2020/10/22 23:25, Joel Fernandes wrote: > On Thu, Oct 22, 2020 at 12:59 AM Li, Aubrey <aubrey...@linux.intel.com> wrote: >> >> On 2020/10/20 9:43, Joel Fernandes (Google) wrote: >>> From: Peter Zijlstra <pet...@infradead.org> >>> >>> Because sched_class::pick_next_task() also implies >>> sched_class::set_next_task() (and possibly put_prev_task() and >>> newidle_balance) it is not state invariant. This makes it unsuitable >>> for remote task selection. >>> >>> Tested-by: Julien Desfossez <jdesfos...@digitalocean.com> >>> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> >>> Signed-off-by: Vineeth Remanan Pillai <vpil...@digitalocean.com> >>> Signed-off-by: Julien Desfossez <jdesfos...@digitalocean.com> >>> Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org> >>> --- >>> kernel/sched/deadline.c | 16 ++++++++++++++-- >>> kernel/sched/fair.c | 32 +++++++++++++++++++++++++++++++- >>> kernel/sched/idle.c | 8 ++++++++ >>> kernel/sched/rt.c | 14 ++++++++++++-- >>> kernel/sched/sched.h | 3 +++ >>> kernel/sched/stop_task.c | 13 +++++++++++-- >>> 6 files changed, 79 insertions(+), 7 deletions(-) >>> >>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >>> index 814ec49502b1..0271a7848ab3 100644 >>> --- a/kernel/sched/deadline.c >>> +++ b/kernel/sched/deadline.c >>> @@ -1848,7 +1848,7 @@ static struct sched_dl_entity >>> *pick_next_dl_entity(struct rq *rq, >>> return rb_entry(left, struct sched_dl_entity, rb_node); >>> } >>> >>> -static struct task_struct *pick_next_task_dl(struct rq *rq) >>> +static struct task_struct *pick_task_dl(struct rq *rq) >>> { >>> struct sched_dl_entity *dl_se; >>> struct dl_rq *dl_rq = &rq->dl; >>> @@ -1860,7 +1860,18 @@ static struct task_struct *pick_next_task_dl(struct >>> rq *rq) >>> dl_se = pick_next_dl_entity(rq, dl_rq); >>> BUG_ON(!dl_se); >>> p = dl_task_of(dl_se); >>> - set_next_task_dl(rq, p, true); >>> + >>> + return p; >>> +} >>> + >>> +static struct task_struct *pick_next_task_dl(struct rq *rq) >>> +{ >>> + struct task_struct *p; >>> + >>> + p = pick_task_dl(rq); >>> + if (p) >>> + set_next_task_dl(rq, p, true); >>> + >>> return p; >>> } >>> >>> @@ -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. > 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. > We tested this series after rebase heavily so it is indeed strange to > see this so late. Cc Hongyu - Maybe we can run the test cases in our hand before next release. Thanks, -Aubrey