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 05:07:50 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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>
Subject: Re: vhost changes (batched) in linux-next after 12/13 trigger random
 crashes in KVM guests after reboot

On Fri, Feb 07, 2020 at 09:53:53AM +0100, Cornelia Huck wrote:
> On Fri, 7 Feb 2020 09:13:14 +0100
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
> > On 07.02.20 08:58, Michael S. Tsirkin wrote:
> > > On Fri, Feb 07, 2020 at 08:47:14AM +0100, Christian Borntraeger wrote:  
> > >> 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(-)
> > >>  
> > > 
> > > 
> > > And the symptom is still the same - random crashes
> > > after a bit of traffic, right?  
> > 
> > random guest crashes after a reboot of the guests. As if vhost would still
> > write into now stale buffers.
> > 
> 
> I'm late to the party; but where is that commit located? Or has it been
> dropped again already?

my vhost tree. Tag batch-v4.