Re: Need help with fixing the Xen waitqueue feature

[Olaf Hering <olaf@aepfle.de>]

On Wed, Nov 23, Keir Fraser wrote:

> Attached three patches for you to try. They apply in sequence.
> 00: A fixed version of "domain_crash on stack overflow"
> 01: Reorders prepare_to_wait so that the vcpu will always be on the
> waitqueue on exit (even if it has just been woken).
> 02: Ensures the vcpu wakes up on the same cpu that it slept on.
> 
> We need all of these. Just need testing to make sure they aren't horribly
> broken. You should be able to test multi-processor host again with these.

Thanks Keir.

In a first test they work ok with multi-processor.
I get vcpu hangs when I balloon up and down with mem-set. Thats most
likely caused by uneven vcpu_pause/unpause calls in my changes which use
wait queue in mem_event handling and ept_get_entry. I will debug that
further.

After the vcpu hung I killed the guest and tried to start a new one.
Oddly enough I wasnt able to fully kill the guest, it remained in --p--d
state. Most vcpus were in paused state before that.

In another attempt I was able to run firefox in a guest. But after
trying to open all "latest headlines" in tabs the guest crashed. qemu-dm
log had alot of this (but nothing in xen dmesg):
track_dirty_vram(f0000000, 12c) failed (-1, 3)

xl vcpu-list shows
(null)                               1     0    -   --p      47.3  any cpu
(null)                               1     1   12   ---      13.4  any cpu
(null)                               1     2    -   --p       4.3  any cpu
(null)                               1     3    -   --p       7.8  any cpu
(null)                               1     4    -   --p       3.5  any cpu
(null)                               1     5    -   --p       1.9  any cpu
(null)                               1     6    -   --p       1.6  any cpu
(null)                               1     7    -   --p       1.4  any cpu

Hmm, qemu-dm doesnt get killed in all cases, killing it destroys the guest..
I have seen that before already.


I will provide more test results tomorrow.


Olaf