Date: Fri, 22 Mar 2024 09:39:11 +0100
From: Igor Raits <igor@...ddata.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org, 
	virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	Stefano Garzarella <sgarzare@...hat.com>, Jaroslav Pulchart <jaroslav.pulchart@...ddata.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: REGRESSION: RIP: 0010:skb_release_data+0xb8/0x1e0 in vhost/tun

Hi Jason,

On Fri, Mar 22, 2024 at 6:31 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Thu, Mar 21, 2024 at 5:44 PM Igor Raits <igor@...ddata.com> wrote:
> >
> > Hello Jason & others,
> >
> > On Wed, Mar 20, 2024 at 10:33 AM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > > On Tue, Mar 19, 2024 at 9:15 PM Igor Raits <igor@...ddata.com> wrote:
> > > >
> > > > Hello Stefan,
> > > >
> > > > On Tue, Mar 19, 2024 at 2:12 PM Stefan Hajnoczi <stefanha@...hat.com> wrote:
> > > > >
> > > > > On Tue, Mar 19, 2024 at 10:00:08AM +0100, Igor Raits wrote:
> > > > > > Hello,
> > > > > >
> > > > > > We have started to observe kernel crashes on 6.7.y kernels (atm we
> > > > > > have hit the issue 5 times on 6.7.5 and 6.7.10). On 6.6.9 where we
> > > > > > have nodes of cluster it looks stable. Please see stacktrace below. If
> > > > > > you need more information please let me know.
> > > > > >
> > > > > > We do not have a consistent reproducer but when we put some bigger
> > > > > > network load on a VM, the hypervisor's kernel crashes.
> > > > > >
> > > > > > Help is much appreciated! We are happy to test any patches.
> > > > >
> > > > > CCing Michael Tsirkin and Jason Wang for vhost_net.
> > > > >
> > > > > >
> > > > > > [62254.167584] stack segment: 0000 [#1] PREEMPT SMP NOPTI
> > > > > > [62254.173450] CPU: 63 PID: 11939 Comm: vhost-11890 Tainted: G
> > > > > >    E      6.7.10-1.gdc.el9.x86_64 #1
> > > > >
> > > > > Are there any patches in this kernel?
> > > >
> > > > Only one, unrelated to this part. Removal of pr_err("EEVDF scheduling
> > > > fail, picking leftmost\n"); line (reported somewhere few months ago
> > > > and it was suggested workaround until proper solution comes).
> > >
> > > Btw, a bisection would help as well.
> >
> > In the end it seems like we don't really have "stable" setup, so
> > bisection looks to be useless but we did find few things meantime:
> >
> > 1. On 6.6.9 it crashes either with unexpected GSO type or usercopy:
> > Kernel memory exposure attempt detected from SLUB object
> > 'skbuff_head_cache'
>
> Do you have a full calltrace for this?

I have shared it in one of the messages in this thread.
https://marc.info/?l=linux-virtualization&m=171085443512001&w=2

> > 2. On 6.7.5, 6.7.10 and 6.8.1 it crashes with RIP:
> > 0010:skb_release_data+0xb8/0x1e0
>
> And for this?

https://marc.info/?l=linux-netdev&m=171083870801761&w=2

> > 3. It does NOT crash on 6.8.1 when VM does not have multi-queue setup
> >
> > Looks like the multi-queue setup (we have 2 interfaces × 3 virtio
> > queues for each) is causing problems as if we set only one queue for
> > each interface the issue is gone.
> > Maybe there is some race condition in __pfx_vhost_task_fn+0x10/0x10 or
> > somewhere around?
>
> I can't tell now, but it seems not because if we have 3 queue pairs we
> will have 3 vhost threads.
>
> > We have noticed that there are 3 of such functions
> > in the stacktrace that gave us hints about what we could try…
>
> Let's try to enable SLUB_DEBUG and KASAN to see if we can get
> something interesting.

We were able to reproduce it even with 1 vhost queue... And now we
have slub_debug + kasan so I hopefully have more useful data for you
now.
I have attached it for better readability.

Thanks!

View attachment "kasan.log" of type "text/x-log" (15173 bytes)

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