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Re: [Xen-devel] [PATCH] xen/sched: fix locking in sched_tick_[suspend|resume]()


  • To: Juergen Gross <jgross@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 4 Oct 2019 08:50:02 +0100
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  • Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>
  • Delivery-date: Fri, 04 Oct 2019 07:50:17 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 04/10/2019 07:40, Juergen Gross wrote:
> sched_tick_suspend() and sched_tick_resume() should not call the
> scheduler specific timer handlers in case the cpu they are running on
> is just being moved to or from a cpupool.
>
> Use a new percpu lock for that purpose.
>
> Reported-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> To be applied on top of my core scheduling series.

There is a somewhat interesting stack trace to go with this

(XEN) Testing NMI watchdog on all CPUs: ok
(XEN) ----[ Xen-4.13.0-8.0.12-d  x86_64  debug=y   Not tainted ]----
(XEN) CPU:    79
(XEN) RIP:    e008:[<ffff82d0802467dc>] set_timer+0x39/0x1f7
(XEN) RFLAGS: 0000000000010002   CONTEXT: hypervisor
<snip>
(XEN) Xen call trace:
(XEN)    [<ffff82d0802467dc>] set_timer+0x39/0x1f7
(XEN)    [<ffff82d08022c1f4>] sched_credit.c#csched_tick_resume+0x54/0x59
(XEN)    [<ffff82d080241dfe>] sched_tick_resume+0x67/0x86
(XEN)    [<ffff82d0802eda52>] mwait-idle.c#mwait_idle+0x32b/0x357
(XEN)    [<ffff82d08027939e>] domain.c#idle_loop+0xa6/0xc2
(XEN)
(XEN) Running stub recovery selftests...
(XEN) Pagetable walk from 0000000000000048:
(XEN) traps.c:1564: GPF (0000): ffff82d0bffff041 [ffff82d0bffff041] ->
ffff82d0803893f2
(XEN)  L4[0x000] = 00000082cfb9c063 ffffffffffffffff
(XEN) traps.c:759: Trap 12: ffff82d0bffff040 [ffff82d0bffff040] ->
ffff82d0803893f2
(XEN)  L3[0x000] = 00000082cfb9b063 ffffffffffffffff
(XEN) traps.c:1098: Trap 3: ffff82d0bffff041 [ffff82d0bffff041] ->
ffff82d0803893f2
(XEN)  L2[0x000] = 00000082cfb9a063 ffffffffffffffff
(XEN)  L1[0x000] = 0000000000000000 ffffffffffffffff
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 79:
(XEN) FATAL PAGE FAULT
(XEN) [error_code=0000]
(XEN) Faulting linear address: 0000000000000048
(XEN) ****************************************

which demonstrates CPU 79 exploding straight out of idle, while the BSP
is continuing to boot.

~Andrew

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