Re: [Xen-devel] null domains after xl destroy

[Juergen Gross <jgross@xxxxxxxx>]

On 19/04/17 03:02, Glenn Enright wrote:
> On 18/04/17 20:36, Juergen Gross wrote:
>> On 12/04/17 00:45, Glenn Enright wrote:
>>> On 12/04/17 10:23, Andrew Cooper wrote:
>>>> On 11/04/2017 23:13, Glenn Enright wrote:
>>>>> On 11/04/17 21:49, Dietmar Hahn wrote:
>>>>>> Am Dienstag, 11. April 2017, 20:03:14 schrieb Glenn Enright:
>>>>>>> On 11/04/17 17:59, Juergen Gross wrote:
>>>>>>>> On 11/04/17 07:25, Glenn Enright wrote:
>>>>>>>>> Hi all
>>>>>>>>>
>>>>>>>>> We are seeing an odd issue with domu domains from xl destroy,
>>>>>>>>> under
>>>>>>>>> recent 4.9 kernels a (null) domain is left behind.
>>>>>>>>
>>>>>>>> I guess this is the dom0 kernel version?
>>>>>>>>
>>>>>>>>> This has occurred on a variety of hardware, with no obvious
>>>>>>>>> commonality.
>>>>>>>>>
>>>>>>>>> 4.4.55 does not show this behavior.
>>>>>>>>>
>>>>>>>>> On my test machine I have the following packages installed under
>>>>>>>>> centos6, from https://xen.crc.id.au/
>>>>>>>>>
>>>>>>>>> ~]# rpm -qa | grep xen
>>>>>>>>> xen47-licenses-4.7.2-4.el6.x86_64
>>>>>>>>> xen47-4.7.2-4.el6.x86_64
>>>>>>>>> kernel-xen-4.9.21-1.el6xen.x86_64
>>>>>>>>> xen47-ocaml-4.7.2-4.el6.x86_64
>>>>>>>>> xen47-libs-4.7.2-4.el6.x86_64
>>>>>>>>> xen47-libcacard-4.7.2-4.el6.x86_64
>>>>>>>>> xen47-hypervisor-4.7.2-4.el6.x86_64
>>>>>>>>> xen47-runtime-4.7.2-4.el6.x86_64
>>>>>>>>> kernel-xen-firmware-4.9.21-1.el6xen.x86_64
>>>>>>>>>
>>>>>>>>> I've also replicated the issue with 4.9.17 and 4.9.20
>>>>>>>>>
>>>>>>>>> To replicate, on a cleanly booted dom0 with one pv VM, I run the
>>>>>>>>> following on the VM
>>>>>>>>>
>>>>>>>>> {
>>>>>>>>> while true; do
>>>>>>>>>  dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
>>>>>>>>> done
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> Then on the dom0 I do this sequence to reliably get a null domain.
>>>>>>>>> This
>>>>>>>>> occurs with oxenstored and xenstored both.
>>>>>>>>>
>>>>>>>>> {
>>>>>>>>> xl sync 1
>>>>>>>>> xl destroy 1
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> xl list then renders something like ...
>>>>>>>>>
>>>>>>>>> (null)                                       1     4     4
>>>>>>>>> --p--d
>>>>>>>>> 9.8     0
>>>>>>>>
>>>>>>>> Something is referencing the domain, e.g. some of its memory pages
>>>>>>>> are
>>>>>>>> still mapped by dom0.
>>>>>>
>>>>>> You can try
>>>>>> # xl debug-keys q
>>>>>> and further
>>>>>> # xl dmesg
>>>>>> to see the output of the previous command. The 'q' dumps domain
>>>>>> (and guest debug) info.
>>>>>> # xl debug-keys h
>>>>>> prints all possible parameters for more informations.
>>>>>>
>>>>>> Dietmar.
>>>>>>
>>>>>
>>>>> I've done this as requested, below is the output.
>>>>>
>>>>> <snip>
>>>>> (XEN) Memory pages belonging to domain 1:
>>>>> (XEN)     DomPage 0000000000071c00: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c01: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c02: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c03: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c04: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c05: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c06: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c07: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c08: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c09: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0a: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0b: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0c: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0d: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0e: caf=00000001, taf=7400000000000001
>>>>> (XEN)     DomPage 0000000000071c0f: caf=00000001, taf=7400000000000001
>>>>
>>>> There are 16 pages still referenced from somewhere.
>>
>> Just a wild guess: could you please try the attached kernel patch? This
>> might give us some more diagnostic data...
>>
>>
>> Juergen
>>
> 
> Thanks Juergen. I applied that, to our 4.9.23 dom0 kernel, which still
> shows the issue. When replicating the leak I now see this trace (via
> dmesg). Hopefully that is useful.
> 
> Please note, I'm going to be offline next week, but am keen to keep on
> with this, it may just be a while before I followup is all.
> 
> Regards, Glenn
> http://rimuhosting.com
> 
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 19 at drivers/block/xen-blkback/xenbus.c:508
> xen_blkbk_remove+0x138/0x140
> Modules linked in: xen_pciback xen_netback xen_gntalloc xen_gntdev
> xen_evtchn xenfs xen_privcmd xt_CT ipt_REJECT nf_reject_ipv4
> ebtable_filter ebtables xt_hashlimit xt_recent xt_state iptable_security
> iptable_raw igle iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4
> nf_nat_ipv4 nf_nat nf_conntrack iptable_filter ip_tables bridge stp llc
> ipv6 crc_ccitt ppdev parport_pc parport serio_raw sg i2c_i801 i2c_smbus
> i2c_core e1000e ptp p000_edac edac_core raid1 sd_mod ahci libahci floppy
> dm_mirror dm_region_hash dm_log dm_mod
> CPU: 0 PID: 19 Comm: xenwatch Not tainted 4.9.23-1.el6xen.x86_64 #1
> Hardware name: Supermicro PDSML/PDSML+, BIOS 6.00 08/27/2007
>  ffffc90040cfbba8 ffffffff8136b61f 0000000000000013 0000000000000000
>  0000000000000000 0000000000000000 ffffc90040cfbbf8 ffffffff8108007d
>  ffffea0001373fe0 000001fc33394434 ffff880000000001 ffff88004d93fac0
> Call Trace:
>  [<ffffffff8136b61f>] dump_stack+0x67/0x98
>  [<ffffffff8108007d>] __warn+0xfd/0x120
>  [<ffffffff810800bd>] warn_slowpath_null+0x1d/0x20
>  [<ffffffff814ebde8>] xen_blkbk_remove+0x138/0x140
>  [<ffffffff814497f7>] xenbus_dev_remove+0x47/0xa0
>  [<ffffffff814bcfd4>] __device_release_driver+0xb4/0x160
>  [<ffffffff814bd0ad>] device_release_driver+0x2d/0x40
>  [<ffffffff814bbfd4>] bus_remove_device+0x124/0x190
>  [<ffffffff814b93a2>] device_del+0x112/0x210
>  [<ffffffff81448113>] ? xenbus_read+0x53/0x70
>  [<ffffffff814b94c2>] device_unregister+0x22/0x60
>  [<ffffffff814ed7cd>] frontend_changed+0xad/0x4c0
>  [<ffffffff810a974e>] ? schedule_tail+0x1e/0xc0
>  [<ffffffff81449b57>] xenbus_otherend_changed+0xc7/0x140
>  [<ffffffff816f1436>] ? _raw_spin_unlock_irqrestore+0x16/0x20
>  [<ffffffff810a974e>] ? schedule_tail+0x1e/0xc0
>  [<ffffffff81449fe0>] frontend_changed+0x10/0x20
>  [<ffffffff814477fc>] xenwatch_thread+0x9c/0x140
>  [<ffffffff810bffa0>] ? woken_wake_function+0x20/0x20
>  [<ffffffff816ed93a>] ? schedule+0x3a/0xa0
>  [<ffffffff816f1436>] ? _raw_spin_unlock_irqrestore+0x16/0x20
>  [<ffffffff810c0c5d>] ? complete+0x4d/0x60
>  [<ffffffff81447760>] ? split+0xf0/0xf0
>  [<ffffffff810a051d>] kthread+0xcd/0xf0
>  [<ffffffff810a974e>] ? schedule_tail+0x1e/0xc0
>  [<ffffffff810a0450>] ? __kthread_init_worker+0x40/0x40
>  [<ffffffff810a0450>] ? __kthread_init_worker+0x40/0x40
>  [<ffffffff816f1b45>] ret_from_fork+0x25/0x30
> ---[ end trace ee097287c9865a62 ]---

Konrad, Roger,

this was triggered by a debug patch in xen_blkbk_remove():

        if (be->blkif)
-               xen_blkif_disconnect(be->blkif);
+               WARN_ON(xen_blkif_disconnect(be->blkif));

So I guess we need something like xen_blk_drain_io() in case of calls to
xen_blkif_disconnect() which are not allowed to fail (either at the call
sites of xen_blkif_disconnect() or in this function depending on a new
boolean parameter indicating it should wait for outstanding I/Os).

I can try a patch, but I'd appreciate if you could confirm this wouldn't
add further problems...


Juergen


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel