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    SubjectRe: [RFC][PATCH 00/16] sched: Core scheduling
    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@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

    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 ]---

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