Re: [lib/stackdepot] 1cd8ce52c5: BUG:unable_to_handle_page_fault_for_address

[Mike Rapoport]

On Fri, Oct 15, 2021 at 10:27:17AM +0200, Vlastimil Babka wrote:
> On 10/14/21 12:16, Mike Rapoport wrote:
> > On Thu, Oct 14, 2021 at 11:33:03AM +0200, Vlastimil Babka wrote:
> >> On 10/14/21 10:54, kernel test robot wrote:
> >> 
> >> In my local testing of the patch, when stackdepot was initialized through
> >> page owner init, it was using kvmalloc() so slab_is_available() was true.
> >> Looks like the exact order of slab vs page_owner alloc is non-deterministic,
> >> could be arch-dependent or just random ordering of init calls. A wrong order
> >> will exploit the apparent fact that slab_is_available() is not a good
> >> indicator of using memblock vs page allocator, and we would need a better one.
> >> Thoughts?
> > 
> > The order of slab vs page_owner is deterministic, but it is different for
> > FLATMEM and SPARSEMEM. And page_ext_init_flatmem_late() that initializes
> > page_ext for FLATMEM is called exactly between buddy and slab setup:
> 
> Oh, so it was due to FLATMEM, thanks for figuring that out!
> 
> > static void __init mm_init(void)
> > {
> > 	...
> > 
> > 	mem_init();
> > 	mem_init_print_info();
> > 	/* page_owner must be initialized after buddy is ready */
> > 	page_ext_init_flatmem_late();
> > 	kmem_cache_init();
> > 
> > 	...
> > }
> > 
> > I've stared for a while at page_ext init and it seems that the
> > page_ext_init_flatmem_late() can be simply dropped because there is anyway
> > a call to invoke_init_callbacks() in page_ext_init() that is called much
> > later in the boot process.
> 
> Yeah, but page_ext_init() only does something for SPARSEMEM, and is empty on
> FLATMEM. Otherwise it would be duplicating all the work. So I'll just move
> page_ext_init_flatmem_late() below kmem_cache_init() in mm_init().

I hope at some point we'll have cleaner mm_init(), but for now simply
moving page_ext_init_flatmem_late() should work.

> Thanks again!

Welcome :)
 

-- 
Sincerely yours,
Mike.