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

[Michal Hocko <mhocko@kernel.org>]

On Wed 05-12-18 13:38:17, Pingfan Liu wrote:
> On Tue, Dec 4, 2018 at 4:56 PM Michal Hocko <mhocko@kernel.org> wrote:
> >
> > On Tue 04-12-18 16:20:32, 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.
> >
> > I believe we should focus on this. Why does the node have no zonelist
> > even though all zonelists should be initialized already? Maybe this is
> > nr_cpus pecularity and we do not initialize all the existing numa nodes.
> > Or maybe the device is associated to a non-existing node with that
> > setup. A full dmesg might help us here.
> >
> Requiring the machine again, and I got the following without nr_cpus option
> [root@dell-per7425-03 ~]# cd /sys/devices/system/node/
> [root@dell-per7425-03 node]# ls
> has_cpu  has_memory  has_normal_memory  node0  node1  node2  node3
> node4  node5  node6  node7  online  possible  power  uevent
> [root@dell-per7425-03 node]# cat has_cpu
> 0-7
> [root@dell-per7425-03 node]# cat has_memory
> 1,5
> [root@dell-per7425-03 node]# cat online
> 0-7
> [root@dell-per7425-03 node]# cat possible
> 0-7
> And lscpu shows the following numa-cpu info:
> NUMA node0 CPU(s):     0,8,16,24
> NUMA node1 CPU(s):     2,10,18,26
> NUMA node2 CPU(s):     4,12,20,28
> NUMA node3 CPU(s):     6,14,22,30
> NUMA node4 CPU(s):     1,9,17,25
> NUMA node5 CPU(s):     3,11,19,27
> NUMA node6 CPU(s):     5,13,21,29
> NUMA node7 CPU(s):     7,15,23,31
> 
> For the full panic message (I masked some hostname info with xx),
> please see the attachment.
> In a short word, it seems a problem with nr_cpus, if without this
> option, the kernel can bootup correctly.

Yep.
[    0.007418] Early memory node ranges
[    0.007419]   node   1: [mem 0x0000000000001000-0x000000000008efff]
[    0.007420]   node   1: [mem 0x0000000000090000-0x000000000009ffff]
[    0.007422]   node   1: [mem 0x0000000000100000-0x000000005c3d6fff]
[    0.007422]   node   1: [mem 0x00000000643df000-0x0000000068ff7fff]
[    0.007423]   node   1: [mem 0x000000006c528000-0x000000006fffffff]
[    0.007424]   node   1: [mem 0x0000000100000000-0x000000047fffffff]
[    0.007425]   node   5: [mem 0x0000000480000000-0x000000087effffff]

There is clearly no node2. Where did the driver get the node2 from?
-- 
Michal Hocko
SUSE Labs