Re: [PATCH 0/6] mm: make movable onlining suck less

[Reza Arbab]

On Wed, Apr 05, 2017 at 06:34:39PM +0200, Michal Hocko wrote:
> This is really interesting. Because add_memory_resource does the
> following
> 	/* call arch's memory hotadd */
> 	ret = arch_add_memory(nid, start, size);
>
> 	if (ret < 0)
> 		goto error;
>
> 	/* we online node here. we can't roll back from here. */
> 	node_set_online(nid);
>
> so we are setting the node online _after_ arch_add_memory but the code
> which adds those sysfs file is called from
>
> arch_add_memory
>  __add_pages
>    __add_section
>      register_new_memory
>        register_mem_sect_under_node
>          node_online check

Okay, so it turns out the original code ends up creating the sysfs links 
not here, but just a little bit afterwards.

add_memory
 add_memory_resource
   arch_add_memory
     [your quoted stack trace above]
   ...
   set_node_online
   ...
   register_one_node
     link_mem_sections
	register_mem_sect_under_node

The reason they're not getting created now is because 
NODE_DATA(nid)->node_spanned_pages = 0 at this point.

link_mem_sections: nid=1, start_pfn=0x10000, end_pfn=0x10000

This is another uninitialized situation, like the one with 
node_start_pfn which caused my removal crash. Except here I'm not sure 
the correct place to splice in and set it.

--
Reza Arbab