| Message ID | 20170920201714.19817-2-pasha.tatashin@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed 20-09-17 16:17:03, 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, however, we set fields in > register_page_bootmem_info that are subsequently clobbered right after in > free_all_bootmem: > > 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 issue where, currently we do not observe problem as memory > is explicitly 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. Thanks for extending the changelog. This is more informative now. > Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> > Reviewed-by: Steven Sistare <steven.sistare@oracle.com> > Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> > Reviewed-by: Bob Picco <bob.picco@oracle.com> I hope I haven't missed anything but it looks good to me. Acked-by: Michal Hocko <mhocko@suse.com> one nit below > --- > arch/x86/mm/init_64.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 5ea1c3c2636e..30fe22558720 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -1182,12 +1182,17 @@ void __init mem_init(void) > > /* clear_bss() already clear the empty_zero_page */ > > - register_page_bootmem_info(); > - > /* this will put all memory onto the freelists */ > free_all_bootmem(); > after_bootmem = 1; > > + /* Must be done after boot memory is put on freelist, because here we standard code style is to do /* * text starts here > + * 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(); > + > /* Register memory areas for /proc/kcore */ > kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR, > PAGE_SIZE, KCORE_OTHER); > -- > 2.14.1
Hi Michal, > > I hope I haven't missed anything but it looks good to me. > > Acked-by: Michal Hocko <mhocko@suse.com> Thank you for your review. > > one nit below >> --- >> arch/x86/mm/init_64.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c >> index 5ea1c3c2636e..30fe22558720 100644 >> --- a/arch/x86/mm/init_64.c >> +++ b/arch/x86/mm/init_64.c >> @@ -1182,12 +1182,17 @@ void __init mem_init(void) >> >> /* clear_bss() already clear the empty_zero_page */ >> >> - register_page_bootmem_info(); >> - >> /* this will put all memory onto the freelists */ >> free_all_bootmem(); >> after_bootmem = 1; >> >> + /* Must be done after boot memory is put on freelist, because here we > > standard code style is to do > /* > * text starts here OK, will change for both patch 1 and 2. Pasha
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 5ea1c3c2636e..30fe22558720 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -1182,12 +1182,17 @@ void __init mem_init(void) /* clear_bss() already clear the empty_zero_page */ - register_page_bootmem_info(); - /* this will put all memory onto the freelists */ free_all_bootmem(); after_bootmem = 1; + /* 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(); + /* Register memory areas for /proc/kcore */ kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR, PAGE_SIZE, KCORE_OTHER);
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, however, we set fields in register_page_bootmem_info that are subsequently clobbered right after in free_all_bootmem: 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 issue where, currently we do not observe problem as memory is explicitly 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@oracle.com> Reviewed-by: Steven Sistare <steven.sistare@oracle.com> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Bob Picco <bob.picco@oracle.com> --- arch/x86/mm/init_64.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)