Re: [PATCH 6.12.y] mm/page_alloc: fix race condition in unaccepted memory handling

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found matching upstream commit but patch is missing proper reference to it

Found matching upstream commit: fefc075182275057ce607effaa3daa9e6e3bdc73

Status in newer kernel trees:
6.14.y | Not found

Note: The patch differs from the upstream commit:
---
1:  fefc075182275 ! 1:  e5e24c3c382e8 mm/page_alloc: fix race condition in unaccepted memory handling
    @@ Commit message
         Cc: Johannes Weiner <hannes@cmpxchg.org>
         Cc: <stable@vger.kernel.org>    [6.5+]
         Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    -
    - ## mm/internal.h ##
    -@@ mm/internal.h: unsigned long move_page_tables(struct pagetable_move_control *pmc);
    - 
    - #ifdef CONFIG_UNACCEPTED_MEMORY
    - void accept_page(struct page *page);
    --void unaccepted_cleanup_work(struct work_struct *work);
    - #else /* CONFIG_UNACCEPTED_MEMORY */
    - static inline void accept_page(struct page *page)
    - {
    -
    - ## mm/mm_init.c ##
    -@@ mm/mm_init.c: static void __meminit zone_init_free_lists(struct zone *zone)
    - 
    - #ifdef CONFIG_UNACCEPTED_MEMORY
    - 	INIT_LIST_HEAD(&zone->unaccepted_pages);
    --	INIT_WORK(&zone->unaccepted_cleanup, unaccepted_cleanup_work);
    - #endif
    - }
    - 
    +    (cherry picked from commit fefc075182275057ce607effaa3daa9e6e3bdc73)
    +    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
     
      ## mm/page_alloc.c ##
     @@ mm/page_alloc.c: bool has_managed_dma(void)
    @@ mm/page_alloc.c: bool has_managed_dma(void)
     -
      static bool lazy_accept = true;
      
    --void unaccepted_cleanup_work(struct work_struct *work)
    --{
    --	static_branch_dec(&zones_with_unaccepted_pages);
    --}
    --
      static int __init accept_memory_parse(char *p)
    - {
    - 	if (!strcmp(p, "lazy")) {
     @@ mm/page_alloc.c: static bool page_contains_unaccepted(struct page *page, unsigned int order)
      static void __accept_page(struct zone *zone, unsigned long *flags,
      			  struct page *page)
    @@ mm/page_alloc.c: static void __accept_page(struct zone *zone, unsigned long *fla
      
      	__free_pages_ok(page, MAX_PAGE_ORDER, FPI_TO_TAIL);
     -
    --	if (last) {
    --		/*
    --		 * There are two corner cases:
    --		 *
    --		 * - If allocation occurs during the CPU bring up,
    --		 *   static_branch_dec() cannot be used directly as
    --		 *   it causes a deadlock on cpu_hotplug_lock.
    --		 *
    --		 *   Instead, use schedule_work() to prevent deadlock.
    --		 *
    --		 * - If allocation occurs before workqueues are initialized,
    --		 *   static_branch_dec() should be called directly.
    --		 *
    --		 *   Workqueues are initialized before CPU bring up, so this
    --		 *   will not conflict with the first scenario.
    --		 */
    --		if (system_wq)
    --			schedule_work(&zone->unaccepted_cleanup);
    --		else
    --			unaccepted_cleanup_work(&zone->unaccepted_cleanup);
    --	}
    +-	if (last)
    +-		static_branch_dec(&zones_with_unaccepted_pages);
      }
      
      void accept_page(struct page *page)
    @@ mm/page_alloc.c: static bool try_to_accept_memory_one(struct zone *zone)
     -	return static_branch_unlikely(&zones_with_unaccepted_pages);
     -}
     -
    - static bool cond_accept_memory(struct zone *zone, unsigned int order,
    - 			       int alloc_flags)
    + static bool cond_accept_memory(struct zone *zone, unsigned int order)
      {
      	long to_accept, wmark;
      	bool ret = false;
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.12.y       |  Success    |  Success   |