[PANIC, hyperv] BUG: unable to handle kernel paging request at ffff880077800004 (hv_ringbuffer_write)

[KY Srinivasan]

> -----Original Message-----
> From: Sitsofe Wheeler [mailto:sitsofe at gmail.com]
> Sent: Wednesday, August 27, 2014 3:58 PM
> To: KY Srinivasan
> Cc: Dexuan Cui; Greg Kroah-Hartman; Haiyang Zhang;
> devel at linuxdriverproject.org; linux-kernel at vger.kernel.org
> Subject: Re: [PANIC, hyperv] BUG: unable to handle kernel paging request at
> ffff880077800004 (hv_ringbuffer_write)
> 
> On Wed, Aug 27, 2014 at 06:45:55PM +0000, KY Srinivasan wrote:
> >
> > > -----Original Message-----
> > > From: Sitsofe Wheeler [mailto:sitsofe at gmail.com]
> > > Sent: Wednesday, August 27, 2014 9:19 AM
> > >
> > > > BTW, with the patch below, hyperv_fb can work now, BUT,
> > > > *occasionally*,
> > > > storvsc_probe() -> ... -> vmbus_open() -> can fail due to
> > > > HV_STATUS_INVALID_ALIGNMENT...
> > >
> > > I applied your new patch on top of KY's pieces (it applied cleanly)
> > > and while it doesn't blow up, one warning is printed out and the UP
> > > boot seemed to stall after input: TPPS/2 message (but pressing
> > > ctrl-alt-delete allows the system to reboot cleanly).
> >
> > First let me thank you guys for looking into this issue. Looking at
> > your dmesg, it looked like storvsc probe failed as Dexuan had seen.
> > Since the failure appears to be alignment related, perhaps we could
> > test with allocating a page all the time (and getting rid of the
> > kmalloc). Sitsofe, here is a patch based on Dexuan's patch. If this
> > works, I will probably minimize failure cases by pre-allocating
> > per-cpu pages for this.:
> 
> After some modifications to apply on top of your previous patches applying
> this latest patch has cured the issues surrounding hyperv_fb issues on boot.
> The only issue seen on boot now is similar to
> https://lkml.org/lkml/2014/8/19/227 ...

That is good to hear. I was under the impression that this issue would be
resolved with all the cleanup we have done. The last patch-set I posted
earlier today has the fix for vmbus_open  bug that Dexuan had identified.

If you could try with the BUG_ON elimination patch-set I sent out earlier
today with the fix in hv.c that I had sent that would be great.  
> 
> How come previous alignment efforts weren't working out?
I have chosen to always allocate a page and so alignment won't be
an issue. I want to eliminate failure in this path and so, I will most likely
do a per-cpu pre-allocation of this buffer.

Thank you very much for taking the time to help us debug these issues.

Regards,

K. Y
> 
> --
> Sitsofe | http://sucs.org/~sits/