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
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