Re: [Xen-devel] Live-Patch application failure in core-scheduling mode

[Jürgen Groß <jgross@xxxxxxxx>]

On 06.02.20 15:02, Sergey Dyasli wrote:
> On 06/02/2020 11:05, Sergey Dyasli wrote:
> > On 06/02/2020 09:57, Jürgen Groß wrote:
> > > On 05.02.20 17:03, Sergey Dyasli wrote:
> > > > Hello,
> > > >
> > > > I'm currently investigating a Live-Patch application failure in core-
> > > > scheduling mode and this is an example of what I usually get:
> > > > (it's easily reproducible)
> > > >
> > > >       (XEN) [  342.528305] livepatch: lp: CPU8 - IPIing the other 15 CPUs
> > > >       (XEN) [  342.558340] livepatch: lp: Timed out on semaphore in CPU quiesce 
> > > > phase 13/15
> > > >       (XEN) [  342.558343] bad cpus: 6 9
> > > >
> > > >       (XEN) [  342.559293] CPU:    6
> > > >       (XEN) [  342.559562] Xen call trace:
> > > >       (XEN) [  342.559565]    [<ffff82d08023f304>] R 
> > > > common/schedule.c#sched_wait_rendezvous_in+0xa4/0x270
> > > >       (XEN) [  342.559568]    [<ffff82d08023f8aa>] F 
> > > > common/schedule.c#schedule+0x17a/0x260
> > > >       (XEN) [  342.559571]    [<ffff82d080240d5a>] F 
> > > > common/softirq.c#__do_softirq+0x5a/0x90
> > > >       (XEN) [  342.559574]    [<ffff82d080278ec5>] F 
> > > > arch/x86/domain.c#guest_idle_loop+0x35/0x60
> > > >
> > > >       (XEN) [  342.559761] CPU:    9
> > > >       (XEN) [  342.560026] Xen call trace:
> > > >       (XEN) [  342.560029]    [<ffff82d080241661>] R _spin_lock_irq+0x11/0x40
> > > >       (XEN) [  342.560032]    [<ffff82d08023f323>] F 
> > > > common/schedule.c#sched_wait_rendezvous_in+0xc3/0x270
> > > >       (XEN) [  342.560036]    [<ffff82d08023f8aa>] F 
> > > > common/schedule.c#schedule+0x17a/0x260
> > > >       (XEN) [  342.560039]    [<ffff82d080240d5a>] F 
> > > > common/softirq.c#__do_softirq+0x5a/0x90
> > > >       (XEN) [  342.560042]    [<ffff82d080279db5>] F 
> > > > arch/x86/domain.c#idle_loop+0x55/0xb0
> > > >
> > > > The first HT sibling is waiting for the second in the LP-application
> > > > context while the second waits for the first in the scheduler context.
> > > >
> > > > Any suggestions on how to improve this situation are welcome.
> > > Can you test the attached patch, please? It is only tested to boot, so
> > > I did no livepatch tests with it.
> > Thank you for the patch! It seems to fix the issue in my manual testing.
> > I'm going to submit automatic LP testing for both thread/core modes.
> Andrew suggested to test late ucode loading as well and so I did.
> It uses stop_machine() to rendezvous cpus and it failed with a similar
> backtrace for a problematic CPU. But in this case the system crashed
> since there is no timeout involved:
>
>      (XEN) [  155.025168] Xen call trace:
>      (XEN) [  155.040095]    [<ffff82d0802417f2>] R _spin_unlock_irq+0x22/0x30
>      (XEN) [  155.069549]    [<ffff82d08023f3c2>] S 
> common/schedule.c#sched_wait_rendezvous_in+0xa2/0x270
>      (XEN) [  155.109696]    [<ffff82d08023f728>] F 
> common/schedule.c#sched_slave+0x198/0x260
>      (XEN) [  155.145521]    [<ffff82d080240e1a>] F 
> common/softirq.c#__do_softirq+0x5a/0x90
>      (XEN) [  155.180223]    [<ffff82d0803716f6>] F 
> x86_64/entry.S#process_softirqs+0x6/0x20
>
> It looks like your patch provides a workaround for LP case, but other
> cases like stop_machine() remain broken since the underlying issue with
> the scheduler is still there.
And here is the fix for ucode loading (that was in fact the only case
where stop_machine_run() wasn't already called in a tasklet).

I have done a manual test loading new ucode with core scheduling
active.


Juergen

Attachment: 0001-xen-make-sure-stop_machine_run-is-always-called-in-a.patch
Description: Text Data

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