On Thu, 2019-09-05 at 13:55 +1000, Michael Ellerman wrote:

Bart Van Assche [off-list ref] writes:

quoted

On 8/30/19 2:13 PM, Qian Cai wrote:

quoted

https://raw.githubusercontent.com/cailca/linux-mm/master/powerpc.config

Once in a while, booting an IBM POWER9 PowerNV system (8335-GTH) would
generate
a warning in lockdep_register_key() at,

if (WARN_ON_ONCE(static_obj(key)))

because

key = 0xc0000000019ad118
&_stext = 0xc000000000000000
&_end = 0xc0000000049d0000

i.e., it will cause static_obj() returns 1.

(back from a trip)

Hi Qian,

Does this mean that on POWER9 it can happen that a dynamically allocated 
object has an address that falls between &_stext and &_end?

I thought that was true on all arches due to initmem, but seems not.

I guess we have the same problem as s390 and we need to define
arch_is_kernel_initmem_freed().

Actually, it is in the .bss section. The commit 2d4f567103ff ("KVM: PPC:
Introduce kvm_tmp framework") adds kvm_tmp[] into the .bss section and then free
the rest of unused spaces back to the page allocator.

kernel_init
  kvm_guest_init
    kvm_free_tmp
      free_reserved_area
        free_unref_page
          free_unref_page_prepare

Later, alloc_workqueue() happens to allocate some pages from there, and triggers
the warning. Not sure what the best way to solve this.