Re: [PATCH v3] mm: page_alloc: ignore init_on_free=1 for debug_pagealloc=1

On 30.03.21 00:25, Sergei Trofimovich wrote:

On !ARCH_SUPPORTS_DEBUG_PAGEALLOC (like ia64) debug_pagealloc=1 implies page_poison=on:

 if (page_poisoning_enabled() ||
      (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
       debug_pagealloc_enabled()))
         static_branch_enable(&_page_poisoning_enabled);

page_poison=on needs to override init_on_free=1.

Before the change it did not work as expected for the following case:

• have PAGE_POISONING=y
• have page_poison unset
• have !ARCH_SUPPORTS_DEBUG_PAGEALLOC arch (like ia64)
• have init_on_free=1
• have debug_pagealloc=1

That way we get both keys enabled:

• static_branch_enable(&init_on_free);
• static_branch_enable(&_page_poisoning_enabled);

which leads to poisoned pages returned for __GFP_ZERO pages.

After the change we execute only:

• static_branch_enable(&_page_poisoning_enabled);

and ignore init_on_free=1.

Acked-by: Vlastimil Babka vbabka@suse.cz Fixes: 8db26a3d4735 ("mm, page_poison: use static key more efficiently") Cc: stable@vger.kernel.org CC: Andrew Morton akpm@linux-foundation.org CC: linux-mm@kvack.org CC: David Hildenbrand david@redhat.com CC: Andrey Konovalov andreyknvl@gmail.com Link: https://lkml.org/lkml/2021/3/26/443

Signed-off-by: Sergei Trofimovich slyfox@gentoo.org

Change since v2:

• Added 'Fixes:' and 'CC: stable@' suggested by Vlastimil and David

• Renamed local variable to 'page_poisoning_requested' for consistency suggested by David

• Simplified initialization of page_poisoning_requested suggested by David

• Added 'Acked-by: Vlastimil'

  mm/page_alloc.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c index cfc72873961d..4bb3cdfc47f8 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -764,32 +764,36 @@ static inline void clear_page_guard(struct zone *zone, struct page *page, */ void init_mem_debugging_and_hardening(void) {

• bool page_poisoning_requested = false;

+#ifdef CONFIG_PAGE_POISONING

• /*

• * Page poisoning is debug page alloc for some arches. If
  

• * either of those options are enabled, enable poisoning.
  

• */
  

• if (page_poisoning_enabled() ||

•     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
  

•      debug_pagealloc_enabled())) {
  

• static_branch_enable(&_page_poisoning_enabled);
  

• page_poisoning_requested = true;
  

• }

+#endif

• if (_init_on_alloc_enabled_early) {

• if (page_poisoning_enabled())
  

• if (page_poisoning_requested)
  pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
  	"will take precedence over init_on_alloc\n");
  

  else static_branch_enable(&init_on_alloc); } if (_init_on_free_enabled_early) {

• if (page_poisoning_enabled())
  

• if (page_poisoning_requested)
  pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
  	"will take precedence over init_on_free\n");
  

  else static_branch_enable(&init_on_free); }

-#ifdef CONFIG_PAGE_POISONING

• /*

• * Page poisoning is debug page alloc for some arches. If
  

• * either of those options are enabled, enable poisoning.
  

• */
  

• if (page_poisoning_enabled() ||

•     (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
  

•      debug_pagealloc_enabled()))
  

• static_branch_enable(&_page_poisoning_enabled);
  

-#endif

• #ifdef CONFIG_DEBUG_PAGEALLOC if (!debug_pagealloc_enabled()) return;

Thanks!

Reviewed-by: David Hildenbrand david@redhat.com