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

On 11.02.20 10:07, Sergey Dyasli wrote:
On 07/02/2020 08:04, Jürgen Groß wrote:
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:

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 
       (XEN) [  342.559568]    [<ffff82d08023f8aa>] F 
       (XEN) [  342.559571]    [<ffff82d080240d5a>] F 
       (XEN) [  342.559574]    [<ffff82d080278ec5>] F 

       (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 
       (XEN) [  342.560036]    [<ffff82d08023f8aa>] F 
       (XEN) [  342.560039]    [<ffff82d080240d5a>] F 
       (XEN) [  342.560042]    [<ffff82d080279db5>] F 

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 
      (XEN) [  155.109696]    [<ffff82d08023f728>] F 
      (XEN) [  155.145521]    [<ffff82d080240e1a>] F 
      (XEN) [  155.180223]    [<ffff82d0803716f6>] F 

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

The patch seems to fix the issue, thanks!
Do you plan to post the 2 patches to the ML now for proper review?



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