Linux Virtualization - Jan 2020 - vhost changes (batched) in linux-next after 12/13 trigger random crashes in KVM guests after reboot

On 06.01.20 11:50, Michael S. Tsirkin wrote:
> On Wed, Dec 18, 2019 at 04:59:02PM +0100, Christian Borntraeger wrote:
>> On 18.12.19 16:10, Michael S. Tsirkin wrote:
>>> On Wed, Dec 18, 2019 at 03:43:43PM +0100, Christian Borntraeger
wrote:
>>>> Michael,
>>>>
>>>> with 
>>>> commit db7286b100b503ef80612884453bed53d74c9a16
(refs/bisect/skip-db7286b100b503ef80612884453bed53d74c9a16)
>>>>     vhost: use batched version by default
>>>> plus
>>>> commit 6bd262d5eafcdf8cdfae491e2e748e4e434dcda6 (HEAD,
refs/bisect/bad)
>>>>     Revert "vhost/net: add an option to test new
code"
>>>> to make things compile (your next tree is not easily
bisectable, can you fix that as well?).
>>>
>>> I'll try.
>>>
>>>>
>>>> I get random crashes in my s390 KVM guests after reboot.
>>>> Reverting both patches together with commit decd9b8
"vhost: use vhost_desc instead of vhost_log" to
>>>> make it compile again) on top of linux-next-1218 makes the
problem go away.
>>>>
>>>> Looks like the batched version is not yet ready for prime time.
Can you drop these patches until
>>>> we have fixed the issues?
>>>>
>>>> Christian
>>>>
>>>
>>> Will do, thanks for letting me know.
>>
>> I have confirmed with the initial reporter (internal test team) that
<driver name='qemu'/>
>> with a known to be broken linux next kernel also fixes the problem, so
it is really the
>> vhost changes.
> 
> OK I'm back and trying to make it more bisectable.
> 
> I pushed a new tag "batch-v2".
> It's same code but with this bisect should get more information.
I get the following with this tag

drivers/vhost/net.c: In function ?vhost_net_tx_get_vq_desc?:
drivers/vhost/net.c:574:7: error: implicit declaration of function
?vhost_get_vq_desc_batch?; did you mean ?vhost_get_vq_desc??
[-Werror=implicit-function-declaration]
  574 |   r = vhost_get_vq_desc_batch(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
      |       ^~~~~~~~~~~~~~~~~~~~~~~
      |       vhost_get_vq_desc

On Tue, Jan 07, 2020 at 09:59:16AM +0100, Christian Borntraeger
wrote:
> 
> 
> On 06.01.20 11:50, Michael S. Tsirkin wrote:
> > On Wed, Dec 18, 2019 at 04:59:02PM +0100, Christian Borntraeger wrote:
> >> On 18.12.19 16:10, Michael S. Tsirkin wrote:
> >>> On Wed, Dec 18, 2019 at 03:43:43PM +0100, Christian
Borntraeger wrote:
> >>>> Michael,
> >>>>
> >>>> with 
> >>>> commit db7286b100b503ef80612884453bed53d74c9a16
(refs/bisect/skip-db7286b100b503ef80612884453bed53d74c9a16)
> >>>>     vhost: use batched version by default
> >>>> plus
> >>>> commit 6bd262d5eafcdf8cdfae491e2e748e4e434dcda6 (HEAD,
refs/bisect/bad)
> >>>>     Revert "vhost/net: add an option to test new
code"
> >>>> to make things compile (your next tree is not easily
bisectable, can you fix that as well?).
> >>>
> >>> I'll try.
> >>>
> >>>>
> >>>> I get random crashes in my s390 KVM guests after reboot.
> >>>> Reverting both patches together with commit decd9b8
"vhost: use vhost_desc instead of vhost_log" to
> >>>> make it compile again) on top of linux-next-1218 makes the
problem go away.
> >>>>
> >>>> Looks like the batched version is not yet ready for prime
time. Can you drop these patches until
> >>>> we have fixed the issues?
> >>>>
> >>>> Christian
> >>>>
> >>>
> >>> Will do, thanks for letting me know.
> >>
> >> I have confirmed with the initial reporter (internal test team)
that <driver name='qemu'/>
> >> with a known to be broken linux next kernel also fixes the
problem, so it is really the
> >> vhost changes.
> > 
> > OK I'm back and trying to make it more bisectable.
> > 
> > I pushed a new tag "batch-v2".
> > It's same code but with this bisect should get more information.
> 
> I get the following with this tag
> 
> drivers/vhost/net.c: In function ?vhost_net_tx_get_vq_desc?:
> drivers/vhost/net.c:574:7: error: implicit declaration of function
?vhost_get_vq_desc_batch?; did you mean ?vhost_get_vq_desc??
[-Werror=implicit-function-declaration]
>   574 |   r = vhost_get_vq_desc_batch(tvq, tvq->iov,
ARRAY_SIZE(tvq->iov),
>       |       ^~~~~~~~~~~~~~~~~~~~~~~
>       |       vhost_get_vq_desc
> 
Not sure why but I pushed a wrong commit. Sorry. Should be good now.

-- 
MST

On 07.01.20 10:39, Michael S. Tsirkin wrote:
> On Tue, Jan 07, 2020 at 09:59:16AM +0100, Christian Borntraeger wrote:
>>
>>
>> On 06.01.20 11:50, Michael S. Tsirkin wrote:
>>> On Wed, Dec 18, 2019 at 04:59:02PM +0100, Christian Borntraeger
wrote:
>>>> On 18.12.19 16:10, Michael S. Tsirkin wrote:
>>>>> On Wed, Dec 18, 2019 at 03:43:43PM +0100, Christian
Borntraeger wrote:
>>>>>> Michael,
>>>>>>
>>>>>> with 
>>>>>> commit db7286b100b503ef80612884453bed53d74c9a16
(refs/bisect/skip-db7286b100b503ef80612884453bed53d74c9a16)
>>>>>>     vhost: use batched version by default
>>>>>> plus
>>>>>> commit 6bd262d5eafcdf8cdfae491e2e748e4e434dcda6 (HEAD,
refs/bisect/bad)
>>>>>>     Revert "vhost/net: add an option to test new
code"
>>>>>> to make things compile (your next tree is not easily
bisectable, can you fix that as well?).
>>>>>
>>>>> I'll try.
>>>>>
>>>>>>
>>>>>> I get random crashes in my s390 KVM guests after
reboot.
>>>>>> Reverting both patches together with commit decd9b8
"vhost: use vhost_desc instead of vhost_log" to
>>>>>> make it compile again) on top of linux-next-1218 makes
the problem go away.
>>>>>>
>>>>>> Looks like the batched version is not yet ready for
prime time. Can you drop these patches until
>>>>>> we have fixed the issues?
>>>>>>
>>>>>> Christian
>>>>>>
>>>>>
>>>>> Will do, thanks for letting me know.
>>>>
>>>> I have confirmed with the initial reporter (internal test team)
that <driver name='qemu'/>
>>>> with a known to be broken linux next kernel also fixes the
problem, so it is really the
>>>> vhost changes.
>>>
>>> OK I'm back and trying to make it more bisectable.
>>>
>>> I pushed a new tag "batch-v2".
>>> It's same code but with this bisect should get more
information.
>>
>> I get the following with this tag
>>
>> drivers/vhost/net.c: In function ?vhost_net_tx_get_vq_desc?:
>> drivers/vhost/net.c:574:7: error: implicit declaration of function
?vhost_get_vq_desc_batch?; did you mean ?vhost_get_vq_desc??
[-Werror=implicit-function-declaration]
>>   574 |   r = vhost_get_vq_desc_batch(tvq, tvq->iov,
ARRAY_SIZE(tvq->iov),
>>       |       ^~~~~~~~~~~~~~~~~~~~~~~
>>       |       vhost_get_vq_desc
>>
> 
> Not sure why but I pushed a wrong commit. Sorry. Should be good now.
> 
during bisect:

drivers/vhost/vhost.c: In function ?vhost_get_vq_desc_batch?:
drivers/vhost/vhost.c:2634:8: error: ?id? undeclared (first use in this
function); did you mean ?i??
 2634 |  ret = id;
      |        ^~
      |        i

I changed that to i


The last step then gave me  (on commit 50297a8480b439efc5f3f23088cb2d90b799acef
vhost: use batched version by default)
net enc1: Unexpected TXQ (0) queue failure: -5
in the guest.

bisect log so far:
[cborntra at m83lp52 linux]$ git bisect log
git bisect start
# bad: [3131e79bb9e9892a5a6bd33513de9bc90b20e867] vhost: use vhost_desc instead
of vhost_log
git bisect bad 3131e79bb9e9892a5a6bd33513de9bc90b20e867
# good: [d1281e3a562ec6a08f944a876481dd043ba739b9] virtio-blk: remove
VIRTIO_BLK_F_SCSI support
git bisect good d1281e3a562ec6a08f944a876481dd043ba739b9
# good: [5b00aab5b6332a67e32dace1dcd3a198ab94ed56] vhost: option to fetch
descriptors through an independent struct
git bisect good 5b00aab5b6332a67e32dace1dcd3a198ab94ed56
# good: [5b00aab5b6332a67e32dace1dcd3a198ab94ed56] vhost: option to fetch
descriptors through an independent struct
git bisect good 5b00aab5b6332a67e32dace1dcd3a198ab94ed56
# bad: [1414d7ee3d10d2ec2bc4ee652d1d90ec91da1c79] vhost: batching fetches
git bisect bad 1414d7ee3d10d2ec2bc4ee652d1d90ec91da1c79