[CRIU] [PATCH] mount: handle a circular reference in mount tree

[Pavel Emelyanov]

On 09/15/2014 10:41 PM, Christopher Covington wrote:
> On 09/15/2014 08:23 AM, Pavel Emelyanov wrote:
>> On 09/12/2014 03:41 PM, Andrey Vagin wrote:
>>> $ cat /proc/self/mountinfo
>>> ...
>>> 1 1 0:2 / / rw - rootfs rootfs rw,size=373396k,nr_inodes=93349
>>> ...
>>>
>>> You can see that mnt_id and parent_mnt_id are equals here.
>>> This patch interpretes this case as a root mount in a tree.
>>
>> While I agree with the patch, I'd like to get some info about
>> how this all happens from the kernel objects perspective.
>>
>> The kernel's show_mountinfo() prints this like
>> seq_printf(m, "%i %i %u:%u ", r->mnt_id, r->mnt_parent->mnt_id,
>>
>> which means, that each mnt always has a parent.
>>
>> We've typically seen the 0 as root's parent. Where did the kernel
>> get this mount from?
> 
> I've only seen this happen on the initramfs.

You mean the 0th parent? This is what I see on my laptop:

35 0 253:0 / / rw,relatime shared:1 - ext4 /dev/mapper/vg_xemulnb-lv_root rw,data=ordered

and pretty much the same in VM with criu

35 0 253:1 / / rw,relatime shared:1 - ext4 /dev/mapper/fedora-root rw,data=ordered

Thanks,
Pavel