Date:   Sat, 15 Jul 2017 03:37:26 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     Frederic Weisbecker <fweisbec@...il.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Wanpeng Li <kernellwp@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Rik van Riel" <riel@...hat.com>
Subject: Re: [PATCH 5/5] sched: Accumulate vtime on top of nsec clocksource

On Thu, Jun 29, 2017 at 07:15:11PM +0200, Frederic Weisbecker wrote:
>From: Wanpeng Li <kernellwp@...il.com>
>
>Currently the cputime source used by vtime is jiffies. When we cross
>a context boundary and jiffies have changed since the last snapshot, the
>pending cputime is accounted to the switching out context.
>
>This system works ok if the ticks are not aligned across CPUs. If they
>instead are aligned (ie: all fire at the same time) and the CPUs run in
>userspace, the jiffies change is only observed on tick exit and therefore
>the user cputime is accounted as system cputime. This is because the
>CPU that maintains timekeeping fires its tick at the same time as the
>others. It updates jiffies in the middle of the tick and the other CPUs
>see that update on IRQ exit:
>
>    CPU 0 (timekeeper)                  CPU 1
>    -------------------              -------------
>                      jiffies = N
>    ...                              run in userspace for a jiffy
>    tick entry                       tick entry (sees jiffies = N)
>    set jiffies = N + 1
>    tick exit                        tick exit (sees jiffies = N + 1)
>                                                account 1 jiffy as stime
>
>Fix this with using a nanosec clock source instead of jiffies. The
>cputime is then accumulated and flushed everytime the pending delta
>reaches a jiffy in order to mitigate the accounting overhead.
>
>[fweisbec: changelog, rebase on struct vtime, field renames, add delta
>on cputime readers, keep idle vtime as-is (low overhead accounting),
>harmonize clock sources]
>
>Reported-by: Luiz Capitulino <lcapitulino@...hat.com>
>Suggested-by: Thomas Gleixner <tglx@...utronix.de>
>Not-Yet-Signed-off-by: Wanpeng Li <kernellwp@...il.com>
>Cc: Rik van Riel <riel@...hat.com>
>Cc: Peter Zijlstra <peterz@...radead.org>
>Cc: Thomas Gleixner <tglx@...utronix.de>
>Cc: Wanpeng Li <kernellwp@...il.com>
>Cc: Ingo Molnar <mingo@...nel.org>
>Cc: Luiz Capitulino <lcapitulino@...hat.com>
>Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Hi all,

This patch seems to be causing this:

BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u9:0/6
caller is debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
CPU: 1 PID: 6 Comm: kworker/u9:0 Not tainted 4.12.0-next-20170714 #187
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
Workqueue: events_unbound call_usermodehelper_exec_work
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x11d/0x1ef lib/dump_stack.c:52
 check_preemption_disabled+0x1f4/0x200 lib/smp_processor_id.c:46
 debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
 vtime_delta.isra.6+0x11/0x60 kernel/sched/cputime.c:686
 task_cputime+0x3ca/0x790 kernel/sched/cputime.c:882
 thread_group_cputime+0x51a/0xaa0 kernel/sched/cputime.c:327
 thread_group_cputime_adjusted+0x73/0xf0 kernel/sched/cputime.c:676
 wait_task_zombie kernel/exit.c:1114 [inline]
 wait_consider_task+0x1c82/0x37f0 kernel/exit.c:1389
 do_wait_thread kernel/exit.c:1452 [inline]
 do_wait+0x457/0xb00 kernel/exit.c:1523
 kernel_wait4+0x1fd/0x380 kernel/exit.c:1665
 SYSC_wait4+0x145/0x160 kernel/exit.c:1677
 SyS_wait4+0x2c/0x40 kernel/exit.c:1673
 call_usermodehelper_exec_sync kernel/kmod.c:286 [inline]
 call_usermodehelper_exec_work+0x1fc/0x2c0 kernel/kmod.c:323
 process_one_work+0xae7/0x1a00 kernel/workqueue.c:2097
 worker_thread+0x221/0x1860 kernel/workqueue.c:2231
 kthread+0x35f/0x430 kernel/kthread.c:231
 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:425
capability: warning: `syz-executor5' uses 32-bit capabilities (legacy support in use)
BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor6/7013
caller is debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
CPU: 3 PID: 7013 Comm: syz-executor6 Not tainted 4.12.0-next-20170714 #187
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x11d/0x1ef lib/dump_stack.c:52
 check_preemption_disabled+0x1f4/0x200 lib/smp_processor_id.c:46
 debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
 vtime_delta.isra.6+0x11/0x60 kernel/sched/cputime.c:686
 task_cputime+0x3ca/0x790 kernel/sched/cputime.c:882
 thread_group_cputime+0x51a/0xaa0 kernel/sched/cputime.c:327
 thread_group_cputime_adjusted+0x73/0xf0 kernel/sched/cputime.c:676
 wait_task_zombie kernel/exit.c:1114 [inline]
 wait_consider_task+0x1c82/0x37f0 kernel/exit.c:1389
 do_wait_thread kernel/exit.c:1452 [inline]
 do_wait+0x457/0xb00 kernel/exit.c:1523
 kernel_wait4+0x1fd/0x380 kernel/exit.c:1665
 SYSC_wait4+0x145/0x160 kernel/exit.c:1677
 SyS_wait4+0x2c/0x40 kernel/exit.c:1673
 do_syscall_64+0x267/0x740 arch/x86/entry/common.c:284
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x40bd8a
RSP: 002b:00007ffdbdf67b08 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 0000000000b22914 RCX: 000000000040bd8a
RDX: 0000000040000001 RSI: 00007ffdbdf67b4c RDI: ffffffffffffffff
RBP: 0000000000002243 R08: 0000000000001b65 R09: 0000000000b22940
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffdbdf67b4c R14: 0000000000016ee4 R15: 0000000000000016
BUG: using smp_processor_id() in preemptible [00000000] code: init/1
caller is debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
CPU: 3 PID: 1 Comm: init Not tainted 4.12.0-next-20170714 #187
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x11d/0x1ef lib/dump_stack.c:52
 check_preemption_disabled+0x1f4/0x200 lib/smp_processor_id.c:46
 debug_smp_processor_id+0x1c/0x20 lib/smp_processor_id.c:56
 vtime_delta.isra.6+0x11/0x60 kernel/sched/cputime.c:686
 task_cputime+0x3ca/0x790 kernel/sched/cputime.c:882
 thread_group_cputime+0x51a/0xaa0 kernel/sched/cputime.c:327
 thread_group_cputime_adjusted+0x73/0xf0 kernel/sched/cputime.c:676
 wait_task_zombie kernel/exit.c:1114 [inline]
 wait_consider_task+0x1c82/0x37f0 kernel/exit.c:1389
 do_wait_thread kernel/exit.c:1452 [inline]
 do_wait+0x457/0xb00 kernel/exit.c:1523
 kernel_wait4+0x1fd/0x380 kernel/exit.c:1665
 SYSC_wait4+0x145/0x160 kernel/exit.c:1677
 SyS_wait4+0x2c/0x40 kernel/exit.c:1673
 do_syscall_64+0x267/0x740 arch/x86/entry/common.c:284
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7f61952dca3e
RSP: 002b:00007fff93bafea0 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 00007f6195c326a0 RCX: 00007f61952dca3e
RDX: 0000000000000001 RSI: 00007fff93bafedc RDI: ffffffffffffffff
RBP: 00007fff93bafedc R08: 00007fff93bb0870 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 00007fff93bb0bd0 R14: 0000000000000000 R15: 0000000000000000

-- 

Thanks,
Sasha

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