Re: [PATCH] mm/alloc: fallback to first node if the wanted node offline

[Pingfan Liu <kernelfans@gmail.com>]

On Tue, Dec 4, 2018 at 4:40 PM Wei Yang <richard.weiyang@gmail.com> wrote:
>
> On Tue, Dec 04, 2018 at 04:20:32PM +0800, Pingfan Liu wrote:
> >On Tue, Dec 4, 2018 at 3:22 PM Michal Hocko <mhocko@kernel.org> wrote:
> >>
> >> On Tue 04-12-18 11:05:57, Pingfan Liu wrote:
> >> > During my test on some AMD machine, with kexec -l nr_cpus=x option, the
> >> > kernel failed to bootup, because some node's data struct can not be allocated,
> >> > e.g, on x86, initialized by init_cpu_to_node()->init_memory_less_node(). But
> >> > device->numa_node info is used as preferred_nid param for
> >> > __alloc_pages_nodemask(), which causes NULL reference
> >> >   ac->zonelist = node_zonelist(preferred_nid, gfp_mask);
> >> > This patch tries to fix the issue by falling back to the first online node,
> >> > when encountering such corner case.
> >>
> >> We have seen similar issues already and the bug was usually that the
> >> zonelists were not initialized yet or the node is completely bogus.
> >> Zonelists should be initialized by build_all_zonelists quite early so I
> >> am wondering whether the later is the case. What is the actual node
> >> number the device is associated with?
> >>
> >The device's node num is 2. And in my case, I used nr_cpus param. Due
> >to init_cpu_to_node() initialize all the possible node.  It is hard
> >for me to figure out without this param, how zonelists is accessed
> >before page allocator works.
>
> If my understanding is correct, we can't do page alloc before zonelist
> is initialized.
>
> I guess Michal's point is to figure out this reason.
>
Yeah, I know. I just want to emphasize that I hit this bug using
nr_cpus, which may be rarely used by people. Hence it may be a
different bug as Michal had seen. Sorry for bad English if it cause
confusion.

Thanks

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