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Subject: Re: divide error: 0000 [#1] SMP in task_numa_migrate -
 handle_mm_fault vanilla 4.4.6
To: Greg KH <greg@kroah.com>
References: <56EAF98B.50605@profihost.ag> <20160317184514.GA6141@kroah.com>
 <56EDD206.3070202@suse.cz> <56EF15BB.3080509@profihost.ag>
 <20160320214130.GB23920@kroah.com>
Cc: Vlastimil Babka <vbabka@suse.cz>, LKML <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>, linux-mm@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Rik van Riel <riel@redhat.com>
From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
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Date: Mon, 21 Mar 2016 11:52:23 +0100
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Am 20.03.2016 um 22:41 schrieb Greg KH:
> On Sun, Mar 20, 2016 at 10:27:23PM +0100, Stefan Priebe wrote:
>>
>> Am 19.03.2016 um 23:26 schrieb Vlastimil Babka:
>>> On 03/17/2016 07:45 PM, Greg KH wrote:
>>>> On Thu, Mar 17, 2016 at 07:38:03PM +0100, Stefan Priebe wrote:
>>>>> Hi,
>>>>>
>>>>> while running qemu 2.5 on a host running 4.4.6 the host system has
>>>>> crashed
>>>>> (load > 200) 3 times in the last 3 days.
>>>>>
>>>>> Always with this stack trace: (copy left here:
>>>>> http://pastebin.com/raw/bCWTLKyt)
>>>>>
>>>>> [69068.874268] divide error: 0000 [#1] SMP
>>>>> [69068.875242] Modules linked in: ebtable_filter ebtables ip6t_REJECT
>>>>> nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter
>>>>> ip6_tables
>>>>> ipt_REJECT nf_reject_ipv4 xt_physdev xt_comment nf_conntrack_ipv4
>>>>> nf_defrag_ipv4 xt_tcpudp xt_mark xt_set xt_addrtype xt_conntrack
>>>>> nf_conntrack ip_set_hash_net ip_set vhost_net tun vhost macvtap macvlan
>>>>> kvm_intel nfnetlink_log kvm nfnetlink irqbypass netconsole dlm
>>>>> xt_multiport
>>>>> iptable_filter ip_tables x_tables iscsi_tcp libiscsi_tcp libiscsi
>>>>> scsi_transport_iscsi nfsd auth_rpcgss oid_registry bonding coretemp
>>>>> 8021q
>>>>> garp fuse i2c_i801 i7core_edac edac_core i5500_temp button btrfs xor
>>>>> raid6_pq dm_mod raid1 md_mod usb_storage ohci_hcd bcache sg usbhid
>>>>> sd_mod
>>>>> ata_generic uhci_hcd ehci_pci ehci_hcd usbcore ata_piix usb_common igb
>>>>> i2c_algo_bit mpt3sas raid_class ixgbe scsi_transport_sas i2c_core
>>>>> mdio ptp
>>>>> pps_core
>>>>> [69068.895604] CPU: 14 PID: 6673 Comm: ceph-osd Not tainted
>>>>> 4.4.6+7-ph #1
>>>>> [69068.897052] Hardware name: Supermicro X8DT3/X8DT3, BIOS 2.1
>>>>> 03/17/2012
>>>>> [69068.898578] task: ffff880fc7f28000 ti: ffff880fda2c4000 task.ti:
>>>>> ffff880fda2c4000
>>>>> [69068.900377] RIP: 0010:[<ffffffff860b372c>]  [<ffffffff860b372c>]
>>>>> task_h_load+0xcc/0x100
>>>
>>> decodecode says:
>>>
>>>   27:   48 83 c1 01             add    $0x1,%rcx
>>>   2b:*  48 f7 f1                div    %rcx             <-- trapping
>>> instruction
>>>
>>> This suggests the CONFIG_FAIR_GROUP_SCHED version of task_h_load:
>>>
>>>         update_cfs_rq_h_load(cfs_rq);
>>>         return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
>>>                         cfs_rq_load_avg(cfs_rq) + 1);
>>>
>>> So the load avg is -1, thus after adding 1 we get division by 0, huh?
>>
>> Yes CONFIG_FAIR_GROUP_SCHED is set. I cherry picked now all those commits up
>> to 4.5 for fair.c:
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/log/kernel/sched/fair.c?h=v4.5
>>
>> It didn't happen again with v4.4.6 + 4.5 patches for fair.c
> 
> Ok, that's a lot of patches, how about figuring out which single patch,
> or shortest number of patches, makes things work again?

will do so but it seems most out of those 9 patches are based on each
other. So it wouldn't be easy.

Stefan

> 
> thanks,
> 
> greg k-h
>