Re: [PATCH v9 02/12] sparc64/mm: setting fields in deferred pages

[Michal Hocko]

On Wed 20-09-17 16:17:04, Pavel Tatashin wrote:
> Without deferred struct page feature (CONFIG_DEFERRED_STRUCT_PAGE_INIT),
> flags and other fields in "struct page"es are never changed prior to first
> initializing struct pages by going through __init_single_page().
> 
> With deferred struct page feature enabled there is a case where we set some
> fields prior to initializing:
> 
> mem_init() {
>      register_page_bootmem_info();
>      free_all_bootmem();
>      ...
> }
> 
> When register_page_bootmem_info() is called only non-deferred struct pages
> are initialized. But, this function goes through some reserved pages which
> might be part of the deferred, and thus are not yet initialized.
> 
> mem_init
> register_page_bootmem_info
> register_page_bootmem_info_node
>  get_page_bootmem
>   .. setting fields here ..
>   such as: page->freelist = (void *)type;
> 
> free_all_bootmem()
> free_low_memory_core_early()
>  for_each_reserved_mem_region()
>   reserve_bootmem_region()
>    init_reserved_page() <- Only if this is deferred reserved page
>     __init_single_pfn()
>      __init_single_page()
>       memset(0) <-- Loose the set fields here
> 
> We end-up with similar issue as in the previous patch, where currently we
> do not observe problem as memory is zeroed. But, if flag asserts are
> changed we can start hitting issues.
> 
> Also, because in this patch series we will stop zeroing struct page memory
> during allocation, we must make sure that struct pages are properly
> initialized prior to using them.
> 
> The deferred-reserved pages are initialized in free_all_bootmem().
> Therefore, the fix is to switch the above calls.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
> Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>

As you separated x86 and sparc patches doing essentially the same I
assume David is going to take this patch?

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  arch/sparc/mm/init_64.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> index 6034569e2c0d..310c6754bcaa 100644
> --- a/arch/sparc/mm/init_64.c
> +++ b/arch/sparc/mm/init_64.c
> @@ -2548,9 +2548,15 @@ void __init mem_init(void)
>  {
>  	high_memory = __va(last_valid_pfn << PAGE_SHIFT);
>  
> -	register_page_bootmem_info();
>  	free_all_bootmem();
>  
> +	/* Must be done after boot memory is put on freelist, because here we
> +	 * might set fields in deferred struct pages that have not yet been
> +	 * initialized, and free_all_bootmem() initializes all the reserved
> +	 * deferred pages for us.
> +	 */
> +	register_page_bootmem_info();
> +
>  	/*
>  	 * Set up the zero page, mark it reserved, so that page count
>  	 * is not manipulated when freeing the page from user ptes.
> -- 
> 2.14.1

-- 
Michal Hocko
SUSE Labs