Re: [PATCH 4/8] v3 Allow memory_block to span multiple memory sections

Dave Hansen
2010-07-20T19:18:15Z

On Mon, 2010-07-19 at 22:55 -0500, Nathan Fontenot wrote:
> +static int add_memory_section(int nid, struct mem_section *section,
> + unsigned long state, enum mem_add_context context)
> +{
> + struct memory_block *mem;
> + int ret = 0;
> +
> + mem = find_memory_block(section);
> + if (mem) {
> + atomic_inc(&mem->section_count);
> + kobject_put(&mem->sysdev.kobj);
> + } else
> + ret = init_memory_block(&mem, section, state);
> +
> if (!ret) {
> - if (context == HOTPLUG)
> + if (context == HOTPLUG &&
> + atomic_read(&mem->section_count) == sections_per_block)
> ret = register_mem_sect_under_node(mem, nid);
> }

I think the atomic_inc() can race with the atomic_dec_and_test() in
remove_memory_block().

Thread 1 does:

mem = find_memory_block(section);

Thread 2 does

atomic_dec_and_test(&mem->section_count);

and destroys the memory block, Thread 1 runs again:

if (mem) {
atomic_inc(&mem->section_count);
kobject_put(&mem->sysdev.kobj);
} else

but now mem got destroyed by Thread 2. You probably need to change
find_memory_block() to itself take a reference, and to use
atomic_inc_unless().

-- Dave