Re: [PATCH memcg v6] net: set proper memcg for net_init hooks allocations

[Shakeel Butt]

On Tue, Jun 7, 2022 at 5:37 AM Vasily Averin <vvs@xxxxxxxxxx> wrote:
>
> On 6/7/22 08:58, Shakeel Butt wrote:
> > On Mon, Jun 6, 2022 at 11:45 AM Vasily Averin <vvs@xxxxxxxxxx> wrote:
> >>
> > [...]
> >>
> >> As far as I understand this report means that 'init_net' have incorrect
> >> virtual address on arm64.
> >
> > So, the two call stacks tell the addresses belong to the kernel
> > modules (nfnetlink and nf_tables) whose underlying memory is allocated
> > through vmalloc and virt_to_page() does not work on vmalloc()
> > addresses.
>
> However in both these cases get_mem_cgroup_from_obj() -> mem_cgroup_from_obj() ->
> virt_to_folio() -> virt_to_page() -> virt_to_pfn() -> __virt_to_phys()
> handles address of struct net taken from for_each_net().
> The only net namespace that exists at this stage is init_net,
> and dmesg output confirms this:
> "virt_to_phys used for non-linear address: ffffd8efe2d2fe00 (init_net)"
>
> >> Roman, Shakeel, I need your help
> >>
> >> Should we perhaps verify kaddr via virt_addr_valid() before using virt_to_page()
> >> If so, where it should be checked?
> >
> > I think virt_addr_valid() check in mem_cgroup_from_obj() should work
> > but I think it is expensive on the arm64 platform. The cheaper and a
> > bit hacky way to avoid such addresses is to directly use
> > is_vmalloc_addr() directly.
>
> I do not understand why you mean that processed address is vmalloc-specific.
> As far as I understand it is valid address of static variable, and for some reason
> arm64 does not consider them valid virtual addresses.
>

Indeed you are right as we are using the addresses of net namespaces
and the report already has the information on the address
ffffd8efe2d2fe00 which is init_net.

I don't know what is the right way to handle such addresses on arm64.
BTW there is a separate report on this issue and arm maintainers are
also CCed. Why not ask this question on that report?