Re: HVM bug: system crashes after offline online a vcpu

[Wei Liu <Wei.Liu2@citrix.com>]

On Wed, 2012-12-19 at 16:04 +0000, Konrad Rzeszutek Wilk wrote:
> On Thu, Dec 13, 2012 at 03:12:17PM +0000, Wei Liu wrote:
> > Hi Konrad
> > 
> > I encountered a bug when trying to bring offline a cpu then online it
> > again in HVM. As I'm not very familiar with HVM stuffs I cannot come up
> > with a quick fix.
> 
> I took your two patches that you posted and they are in v3.8 now.
> 
> It seems that there are bugs in the offline/online code thought.
> 
> I did this:
> # echo 0 > /sys/devices/system/cpu/cpu3/online
> # echo 1 > /sys/devices/system/cpu/cpu3/online
> 
> With a PV guest and it blows up (with or without your patches).
> 
> Have you seen something similar to this:
> 
> [  106.166795] BUG: scheduling while atomic: swapper/2/0/0x00000000
> [  106.167168] microcode: CPU2 sig=0x206a7, pf=0x2, revision=0x17
> [  106.167566] Modules linked in: sg sd_mod dm_multipath dm_mod xen_evtchn iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi scsi_mod libcrc32c crc32c radeon fbcon tileblit font bitblit softcursor ttm drm_kms_helper crc32c_intel xen_blkfront xen_netfront xen_fbfront fb_sys_fops sysimgblt sysfillrect syscopyarea xen_kbdfront xenfs xen_privcmd [last unloaded: dump_dma]
> [  106.169286] Pid: 0, comm: swapper/2 Tainted: G           O 3.5.0-rc3upstream-00139-gb1849b3-dirty #1
> [  106.170152] Call Trace:
> [  106.170598]  [<ffffffff8109bcbd>] __schedule_bug+0x4d/0x60
> [  106.171042]  [<ffffffff815be0fc>] __schedule+0x69c/0x760
> [  106.171469]  [<ffffffff815be284>] schedule+0x24/0x70
> [  106.171890]  [<ffffffff8103fbe9>] cpu_idle+0xc9/0xe0
> [  106.172309]  [<ffffffff81033e79>] ? xen_irq_enable_direct_reloc+0x4/0x4
> [  106.172726]  [<ffffffff815b1c5d>] cpu_bringup_and_idle+0xe/0x10
> [  106.174533] BUG: scheduling while atomic: swapper/2/0/0x00000000
> ?
> 

IIRC I didn't see this. I was using your xen.git kernel tree, not the
upstream one. The PV path was fixed after applying my patch and the HVM
path I didn't have much idea. I didn't play much with online/offline
after fixing what I could fix.

Let me play with upstream kernel and give you some feedback.


Wei