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

[Aaron Lu]

On Mon, Mar 11, 2019 at 05:20:19PM -0700, Greg Kerr wrote:
> On Mon, Mar 11, 2019 at 4:36 PM Subhra Mazumdar
> <subhra.mazumdar@xxxxxxxxxx> 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@xxxxxxxxxx> 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

Probably due to SMT not enabled for this qemu setup.

rq->core can be NULL for cpu0: sched_cpu_starting() won't be called for
CPU0 and since it doesn't have any siblings, its rq->core remains
un-initialized(NULL).

> [   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 ]---