Re: [Qemu-devel] Problems with qemu "modern" virtio on sparc64

[Guenter Roeck]

On 12/30/2016 10:18 AM, Mark Cave-Ayland wrote:
> On 25/11/16 18:11, Guenter Roeck wrote:
>
> > Hi,
> >
> > I am using virtio on sparc64 for my Linux kernel runtime tests.
> >
> > Starting with qemu v2.7, I noticed that the kernel either gets stuck or
> > crashes.
> > After adding some debug information to the kernel, I found that the
> > problem happens
> > in vp_reset().
> >
> > Interestingly, when running v4.9-rc6 without modification, the kernel
> > crashes on me.
> > If I add pr_info just before and after the vp_iowrite8() in
> > virtio_pci_modern.c:vp_reset(),
> > the kernel gets stuck in the vp_iowrite8().
> >
> > Here is the relevant part of the crash:
> >
> > [    3.151167] Unable to handle kernel NULL pointer dereference
> > [    3.151809] tsk->{mm,active_mm}->context = 0000000000000000
> > [    3.152430] tsk->{mm,active_mm}->pgd = fffff80000402000
> > [    3.153032]               \|/ ____ \|/
> > [    3.153032]               "@'/ .. \`@"
> > [    3.153032]               /_| \__/ |_\
> > [    3.153032]                  \__U_/
> > [    3.154042] swapper(1): Oops [#1]
> > [    3.154773] CPU: 0 PID: 1 Comm: swapper Not tainted 4.9.0-rc5+ #4
> > [    3.155375] task: fffff8001f0af620 task.stack: fffff8001f0b0000
> > [    3.155958] TSTATE: 0000009980001606 TPC: 00000000006edf44 TNPC:
> > 00000000006edf48 Y: 00000000    Not tainted
> > [    3.156901] TPC: <vp_reset+0x4/0x40>
> >
> > None of the pointers used in vp_reset() is NULL. As mentioned above,
> > adding a pr_info
> > just before vp_iowrite8() makes the crash disappear and the kernel is
> > stuck instead.
> > Here is how it looks like:
> >
> > [    3.104243] Hi there
> > [   26.912509] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 23s!
> > [swapper:1]
> > [   26.913102] Modules linked in:
> > [   26.914061] CPU: 0 PID: 1 Comm: swapper Not tainted 4.9.0-rc5+ #5
> > [   26.914633] task: fffff8001f0af620 task.stack: fffff8001f0b0000
> > [   26.915156] TSTATE: 0000004480001605 TPC: 00000000006edf50 TNPC:
> > 00000000006edf54 Y: 00000412    Not tainted
> > [   26.915954] TPC: <vp_reset+0x10/0x60>
> >
> > Another pr_info() after vp_iowrite8() is never printed, suggesting that
> > the code never
> > gets to that point.
> >
> > The kernel configuration is sparc64_defconfig with the following
> > configuration
> > options enabled.
> >
> > CONFIG_DEVTMPFS=y
> > CONFIG_VIRTIO=y
> > CONFIG_VIRTIO_PCI=y
> > CONFIG_VIRTIO_BLK=y
> > CONFIG_VIRTIO_NET=y
> > CONFIG_VIRTIO_BALLOON=y
> > CONFIG_VIRTIO_CONSOLE=y
> > CONFIG_SCSI_VIRTIO=y
> >
> > Command line is
> >
> > qemu-system-sparc64 -M sun4u -cpu "TI UltraSparc IIi" -m 512 \
> >     -drive file=simple-root-filesystem-sparc.ext3,if=virtio,format=raw \
> >     -kernel arch/sparc/boot/image -no-reboot \
> >     -append "root=/dev/vda init=/sbin/init.sh console=ttyS0" \
> >     -nographic -monitor none
> >
> > Does anyone have an idea what might be wrong ?
> >
> > Thanks,
> > Guenter
>
> Hi Guenter,
>
> Have you been able to investigate this issue any further? Does the 2.8
> release solve the issue for you?

I did not make any progress, and reverted to qemu v2.6.

Problem is still seen with v2.8 (release); it crashes. The recent virtio
related patch does not make a difference. v2.7.1 also still crashes.
Only difference with both versions is the crash traceback.

Guenter