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

[Aubrey Li]

On Tue, Mar 12, 2019 at 3:45 PM Aubrey Li <aubrey.intel@xxxxxxxxx> wrote:
>
> On Tue, Mar 12, 2019 at 7:36 AM 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,
>
> One more NULL pointer dereference:
>
> Mar 12 02:24:46 aubrey-ivb kernel: [  201.916741] core sched enabled
> [  201.950203] BUG: unable to handle kernel NULL pointer dereference
> at 0000000000000008
> [  201.950254] ------------[ cut here ]------------
> [  201.959045] #PF error: [normal kernel read fault]
> [  201.964272] !se->on_rq
> [  201.964287] WARNING: CPU: 22 PID: 2965 at kernel/sched/fair.c:6849
> set_next_buddy+0x52/0x70

A quick workaround below:

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1d0dac4fd94f..ef6acfe2cf7d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6834,7 +6834,7 @@ static void set_last_buddy(struct sched_entity *se)
                return;

        for_each_sched_entity(se) {
-               if (SCHED_WARN_ON(!se->on_rq))
+               if (SCHED_WARN_ON(!(se && se->on_rq))
                        return;
                cfs_rq_of(se)->last = se;
        }
@@ -6846,7 +6846,7 @@ static void set_next_buddy(struct sched_entity *se)
                return;

        for_each_sched_entity(se) {
-               if (SCHED_WARN_ON(!se->on_rq))
+               if (SCHED_WARN_ON(!(se && se->on_rq))
                        return;
                cfs_rq_of(se)->next = se;
        }

And now I'm running into a hard LOCKUP:

[  326.336279] NMI watchdog: Watchdog detected hard LOCKUP on cpu 31
[  326.336280] Modules linked in: ipt_MASQUERADE xfrm_user xfrm_algo
iptable_nat nf_nat_ipv4 xt_addrtype iptable_filter ip_tables
xt_conntrack x_tables nf_nat nf_conntracki
[  326.336311] irq event stamp: 164460
[  326.336312] hardirqs last  enabled at (164459):
[<ffffffff810c7a97>] sched_core_balance+0x247/0x470
[  326.336312] hardirqs last disabled at (164460):
[<ffffffff810c7963>] sched_core_balance+0x113/0x470
[  326.336313] softirqs last  enabled at (164250):
[<ffffffff81e00359>] __do_softirq+0x359/0x40a
[  326.336314] softirqs last disabled at (164213):
[<ffffffff81095be1>] irq_exit+0xc1/0xd0
[  326.336315] CPU: 31 PID: 0 Comm: swapper/31 Tainted: G          I
    5.0.0-rc8-00542-gd697415be692-dirty #15
[  326.336316] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS
SE5C600.86B.99.99.x058.082120120902 08/21/2012
[  326.336317] RIP: 0010:native_queued_spin_lock_slowpath+0x18f/0x1c0
[  326.336318] Code: c1 ee 12 83 e0 03 83 ee 01 48 c1 e0 05 48 63 f6
48 05 80 51 1e 00 48 03 04 f5 40 58 39 82 48 89 10 8b 42 08 85 c0 75
09 f3 90 <8b> 42 08 85 c0 74 f7 4b
[  326.336318] RSP: 0000:ffffc9000643bd58 EFLAGS: 00000046
[  326.336319] RAX: 0000000000000000 RBX: ffff888c0ade4400 RCX: 0000000000800000
[  326.336320] RDX: ffff88980bbe5180 RSI: 0000000000000019 RDI: ffff888c0ade4400
[  326.336321] RBP: ffff888c0ade4400 R08: 0000000000800000 R09: 00000000001e3a80
[  326.336321] R10: ffffc9000643bd08 R11: 0000000000000000 R12: 0000000000000000
[  326.336322] R13: 0000000000000000 R14: ffff88980bbe4400 R15: 000000000000001f
[  326.336323] FS:  0000000000000000(0000) GS:ffff88980ba00000(0000)
knlGS:0000000000000000
[  326.336323] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  326.336324] CR2: 00007fdcd7fd7728 CR3: 00000017e821a001 CR4: 00000000000606e0
[  326.336325] Call Trace:
[  326.336325]  do_raw_spin_lock+0xab/0xb0
[  326.336326]  _raw_spin_lock+0x4b/0x60
[  326.336326]  double_rq_lock+0x99/0x140
[  326.336327]  sched_core_balance+0x11e/0x470
[  326.336327]  __balance_callback+0x49/0xa0
[  326.336328]  __schedule+0x1113/0x1570
[  326.336328]  schedule_idle+0x1e/0x40
[  326.336329]  do_idle+0x16b/0x2a0
[  326.336329]  cpu_startup_entry+0x19/0x20
[  326.336330]  start_secondary+0x17f/0x1d0
[  326.336331]  secondary_startup_64+0xa4/0xb0
[  330.959367] ---[ end Kernel panic - not syncing: Hard LOCKUP ]---