linux-kernel - Re: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq

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Message-Id: <33118425-8548-475A-8DED-9A2424C0BCCC@linux.vnet.ibm.com>
Date:   Tue, 31 Jan 2017 16:30:12 +0530
From:   Sachin Sant <sachinp@...ux.vnet.ibm.com>
To:     Matt Fleming <matt@...eblueprint.co.uk>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        peterz@...radead.org,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [tip:sched/core] sched/core: Add debugging code to catch missing
 update_rq_clock() calls

Trimming the cc list.

>> I assume I should be worried?
> 
> Thanks for the report. No need to worry, the bug has existed for a
> while, this patch just turns on the warning ;-)
> 
> The following commit queued up in tip/sched/core should fix your
> issues (assuming you see the same callstack on all your powerpc
> machines):
> 
>  https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=sched/core&id=1b1d62254df0fe42a711eb71948f915918987790

I still see this warning with today’s next running inside PowerVM LPAR
on a POWER8 box. The stack trace is different from what Michael had
reported.

Easiest way to recreate this is to Online/offline cpu’s.

[  114.795609] rq->clock_update_flags < RQCF_ACT_SKIP
[  114.795621] ------------[ cut here ]------------
[  114.795632] WARNING: CPU: 2 PID: 27 at kernel/sched/sched.h:804 set_next_entity+0xbc8/0xcc0
[  114.795634] Modules linked in: xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc rpadlpar_io rpaphp kvm_pr kvm ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter dccp_diag dccp tcp_diag udp_diag inet_diag unix_diag af_packet_diag netlink_diag rpcrdma ib_isert iscsi_target_mod ib_iser libiscsi scsi_transport_iscsi ib_srpt target_core_mod ib_srp ib_ipoib rdma_ucm ib_ucm ib_uverbs ib_umad rdma_cm ib_cm iw_cm iw_cxgb3 ib_core ghash_generic xts gf128mul tpm_ibmvtpm tpm sg vmx_crypto pseries_rng nfsd auth_rpcgss nfs_acl lockd grace sunrpc binfmt_misc ip_tables xfs libcrc32c sr_mod sd_mod cdrom cxgb3 ibmvscsi ibmveth scsi_transport_srp mdio
[  114.795751]  dm_mirror dm_region_hash dm_log dm_mod
[  114.795762] CPU: 2 PID: 27 Comm: migration/2 Not tainted 4.10.0-rc6-next-20170131 #1
[  114.795765] task: c0000004fa2f8600 task.stack: c0000004fa49c000
[  114.795768] NIP: c000000000114ed8 LR: c000000000114ed4 CTR: c0000000004a8cf0
[  114.795771] REGS: c0000004fa49f6a0 TRAP: 0700   Not tainted  (4.10.0-rc6-next-20170131)
[  114.795773] MSR: 8000000002823033 <SF,VEC,VSX,FP,ME,IR,DR,RI,LE>
[  114.795787]   CR: 28004022  XER: 00000000
[  114.795789] CFAR: c0000000008ec5c4 SOFTE: 0 
GPR00: c000000000114ed4 c0000004fa49f920 c00000000100dd00 0000000000000026 
GPR04: 0000000000000000 0000000000000006 6574616470755f6b c0000000011cdd00 
GPR08: 0000000000000000 c000000000c6edb0 000000015ef20000 d000000006488538 
GPR12: 0000000000004400 c00000000e801200 c0000000000ecc38 c0000004fe064300 
GPR16: 0000000000000000 0000000000000001 0000000000000000 c000000000f27e08 
GPR20: c000000000f277c5 0000000000000000 0000000000000004 0000000000000000 
GPR24: c00000015fba49f0 c000000000f27e08 c000000000ef9e80 c0000004fa49fb00 
GPR28: c00000015fba4980 c00000015fba49f0 c0000004f34c1000 c00000015fba49f0 
[  114.795850] NIP [c000000000114ed8] set_next_entity+0xbc8/0xcc0
[  114.795855] LR [c000000000114ed4] set_next_entity+0xbc4/0xcc0
[  114.795857] Call Trace:
[  114.795862] [c0000004fa49f920] [c000000000114ed4] set_next_entity+0xbc4/0xcc0 (unreliable)
[  114.795869] [c0000004fa49f9d0] [c000000000119f4c] pick_next_task_fair+0xfc/0x6f0
[  114.795874] [c0000004fa49fae0] [c000000000104820] sched_cpu_dying+0x3c0/0x450
[  114.795880] [c0000004fa49fb80] [c0000000000c1958] cpuhp_invoke_callback+0x148/0x5b0
[  114.795886] [c0000004fa49fbf0] [c0000000000c3340] take_cpu_down+0xb0/0x110
[  114.795893] [c0000004fa49fc50] [c0000000001a1e58] multi_cpu_stop+0x1a8/0x1e0
[  114.795899] [c0000004fa49fca0] [c0000000001a20c4] cpu_stopper_thread+0x104/0x1e0
[  114.795905] [c0000004fa49fd60] [c0000000000f2b90] smpboot_thread_fn+0x290/0x2a0
[  114.795911] [c0000004fa49fdc0] [c0000000000ecd7c] kthread+0x14c/0x190
[  114.795919] [c0000004fa49fe30] [c00000000000b4e8] ret_from_kernel_thread+0x5c/0x74
[  114.795921] Instruction dump:
[  114.795924] 0fe00000 4bfff884 3d02fff2 89289ac5 2f890000 40fef4ec 39200001 3c62ffac 
[  114.795936] 38633698 99289ac5 487d76b5 60000000 <0fe00000> 4bfff4cc eb9f0118 e93f0120 
[  114.795948] ---[ end trace 5c822f32f967fbc5 ]---
[  123.059141] nr_pdflush_threads exported in /proc is scheduled for removal

Thanks
-Sachin