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

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Message-ID: <20200207095353.08bc91e4.cohuck@redhat.com>
Date:   Fri, 7 Feb 2020 09:53:53 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.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, 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?