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

[Steven Haigh <netwiz@xxxxxxxxx>]

On 19/04/17 20:09, Juergen Gross wrote:
> On 19/04/17 09:16, Roger Pau Monné wrote:
>> On Wed, Apr 19, 2017 at 06:39:41AM +0200, Juergen Gross wrote:
>>> On 19/04/17 03:02, Glenn Enright wrote:
>>>> 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...
>>
>> Hello,
>>
>> Thanks for debugging this, the easiest solution seems to be to replace the
>> ring->inflight atomic_read check in xen_blkif_disconnect with a call to
>> xen_blk_drain_io instead, and making xen_blkif_disconnect return void (to
>> prevent further issues like this one).
> 
> Glenn,
> 
> can you please try the attached patch (in dom0)?

For what its worth, I have applied this in kernel package 4.9.23-2 as
follows:

* Wed Apr 19 2017 Steven Haigh <netwiz@xxxxxxxxx> - 4.9.23-2
- xen/blkback: fix disconnect while I/Os in flight

Its available from any 'in sync' mirror:
        https://xen.crc.id.au/downloads/

Feedback welcome for both mine and Juergen's sake.

-- 
Steven Haigh

Email: netwiz@xxxxxxxxx
Web: https://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897

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