Re: [RFC][PATCH 00/16] sched: Core scheduling

Greg Kerr
2019-03-12T00:20:35Z

On Mon, Mar 11, 2019 at 4:36 PM Subhra Mazumdar
<subhra.mazumdar@oracle.com> wrote:
>
>
> On 3/11/19 11:34 AM, Subhra Mazumdar wrote:
> >
> > On 3/10/19 9:23 PM, Aubrey Li wrote:
> >> On Sat, Mar 9, 2019 at 3:50 AM Subhra Mazumdar
> >> <subhra.mazumdar@oracle.com> wrote:
> >>> expected. Most of the performance recovery happens in patch 15 which,
> >>> unfortunately, is also the one that introduces the hard lockup.
> >>>
> >> After applied Subhra's patch, the following is triggered by enabling
> >> core sched when a cgroup is
> >> under heavy load.
> >>
> > It seems you are facing some other deadlock where printk is involved.
> > Can you
> > drop the last patch (patch 16 sched: Debug bits...) and try?
> >
> > Thanks,
> > Subhra
> >
> Never Mind, I am seeing the same lockdep deadlock output even w/o patch
> 16. Btw
> the NULL fix had something missing, following works.

Is this panic below, which occurs when I tag the first process,
related or known? If not, I will debug it tomorrow.

[ 46.831828] BUG: unable to handle kernel NULL pointer dereference
at 0000000000000000
[ 46.831829] core sched enabled
[ 46.834261] #PF error: [WRITE]
[ 46.834899] PGD 0 P4D 0
[ 46.835438] Oops: 0002 [#1] SMP PTI
[ 46.836158] CPU: 0 PID: 11 Comm: migration/0 Not tainted
5.0.0everyday-glory-03949-g2d8fdbb66245-dirty #7
[ 46.838206] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1 04/01/2014
[ 46.839844] RIP: 0010:_raw_spin_lock+0x7/0x20
[ 46.840448] Code: 00 00 00 65 81 05 25 ca 5c 51 00 02 00 00 31 c0
ba ff 00 00 00 f0 0f b1 17 74 05 e9 93 80 46 ff f3 c3 90 31 c0 ba 01
00 00 00 <f0> 0f b1 17 74 07 89 c6 e9 1c 6e 46 ff f3 c3 66 2e 0f 1f 84
00 00
[ 46.843000] RSP: 0018:ffffb9d300cabe38 EFLAGS: 00010046
[ 46.843744] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000004
[ 46.844709] RDX: 0000000000000001 RSI: ffffffffaea435ae RDI: 0000000000000000
[ 46.845689] RBP: ffffb9d300cabed8 R08: 0000000000000000 R09: 0000000000020800
[ 46.846651] R10: ffffffffaf603ea0 R11: 0000000000000001 R12: ffffffffaf6576c0
[ 46.847619] R13: ffff9a57366c8000 R14: ffff9a5737401300 R15: ffffffffade868f0
[ 46.848584] FS: 0000000000000000(0000) GS:ffff9a5737a00000(0000)
knlGS:0000000000000000
[ 46.849680] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 46.850455] CR2: 0000000000000000 CR3: 00000001d36fa000 CR4: 00000000000006f0
[ 46.851415] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 46.852371] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 46.853326] Call Trace:
[ 46.853678] __schedule+0x139/0x11f0
[ 46.854167] ? cpumask_next+0x16/0x20
[ 46.854668] ? cpu_stop_queue_work+0xc0/0xc0
[ 46.855252] ? sort_range+0x20/0x20
[ 46.855742] schedule+0x4e/0x60
[ 46.856171] smpboot_thread_fn+0x12a/0x160
[ 46.856725] kthread+0x112/0x120
[ 46.857164] ? kthread_stop+0xf0/0xf0
[ 46.857661] ret_from_fork+0x35/0x40
[ 46.858146] Modules linked in:
[ 46.858562] CR2: 0000000000000000
[ 46.859022] ---[ end trace e9fff08f17bfd2be ]---

- Greg

>
> --------->8------------
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1d0dac4..27cbc64 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4131,7 +4131,7 @@ 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) {
> @@ -4149,13 +4149,15 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct
> sched_entity *curr)
> /*
> * Prefer last buddy, try to return the CPU to a preempted task.
> */
> - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
> + if (left && cfs_rq->last && wakeup_preempt_entity(cfs_rq->last,
> left)
> + < 1)
> se = cfs_rq->last;
>
> /*
> * Someone really wants this to run. If it's not unfair, run it.
> */
> - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
> + if (left && cfs_rq->next && wakeup_preempt_entity(cfs_rq->next,
> left)
> + < 1)
> se = cfs_rq->next;
>
> clear_buddies(cfs_rq, se);
> @@ -6958,6 +6960,9 @@ pick_task_fair(struct rq *rq)
>
> se = pick_next_entity(cfs_rq, NULL);
>
> + if (!(se || curr))
> + return NULL;
> +
> if (curr) {
> if (se && curr->on_rq)
> update_curr(cfs_rq);
>