linux-kernel - Re: vhost changes (batched) in linux-next after 12/13 trigger random crashes in KVM guests after reboot

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Date:   Fri, 7 Feb 2020 08:47:14 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     eperezma@...hat.com,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: vhost changes (batched) in linux-next after 12/13 trigger random
 crashes in KVM guests after reboot

Also adding Cornelia.


On 06.02.20 23:17, Michael S. Tsirkin wrote:
> On Thu, Feb 06, 2020 at 04:12:21PM +0100, Christian Borntraeger wrote:
>>
>>
>> On 06.02.20 15:22, eperezma@...hat.com wrote:
>>> Hi Christian.
>>>
>>> Could you try this patch on top of ("38ced0208491 vhost: use batched version by default")?
>>>
>>> It will not solve your first random crash but it should help with the lost of network connectivity.
>>>
>>> Please let me know how does it goes.
>>
>>
>> 38ced0208491 + this seem to be ok.
>>
>> Not sure if you can make out anything of this (and the previous git bisect log)
> 
> Yes it does - that this is just bad split-up of patches, and there's
> still a real bug that caused worse crashes :)
> 
> So I just pushed batch-v4.
> I expect that will fail, and bisect to give us
>     vhost: batching fetches
> Can you try that please?
> 

yes.

eccb852f1fe6bede630e2e4f1a121a81e34354ab is the first bad commit
commit eccb852f1fe6bede630e2e4f1a121a81e34354ab
Author: Michael S. Tsirkin <mst@...hat.com>
Date:   Mon Oct 7 06:11:18 2019 -0400

    vhost: batching fetches
    
    With this patch applied, new and old code perform identically.
    
    Lots of extra optimizations are now possible, e.g.
    we can fetch multiple heads with copy_from/to_user now.
    We can get rid of maintaining the log array.  Etc etc.
    
    Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

 drivers/vhost/test.c  |  2 +-
 drivers/vhost/vhost.c | 39 ++++++++++++++++++++++++++++++++++-----
 drivers/vhost/vhost.h |  4 +++-
 3 files changed, 38 insertions(+), 7 deletions(-)


>