From 98fdd2f612e949c652693f6df00442c81037776d Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Tue, 6 May 2025 16:32:07 +0300 Subject: [PATCH] mm/page_alloc: fix race condition in unaccepted memory handling commit fefc075182275057ce607effaa3daa9e6e3bdc73 upstream. The page allocator tracks the number of zones that have unaccepted memory using static_branch_enc/dec() and uses that static branch in hot paths to determine if it needs to deal with unaccepted memory. Borislav and Thomas pointed out that the tracking is racy: operations on static_branch are not serialized against adding/removing unaccepted pages to/from the zone. Sanity checks inside static_branch machinery detects it: WARNING: CPU: 0 PID: 10 at kernel/jump_label.c:276 __static_key_slow_dec_cpuslocked+0x8e/0xa0 The comment around the WARN() explains the problem: /* * Warn about the '-1' case though; since that means a * decrement is concurrent with a first (0->1) increment. IOW * people are trying to disable something that wasn't yet fully * enabled. This suggests an ordering problem on the user side. */ The effect of this static_branch optimization is only visible on microbenchmark. Instead of adding more complexity around it, remove it altogether. Link: https://lkml.kernel.org/r/20250506133207.1009676-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory") Link: https://lore.kernel.org/all/20250506092445.GBaBnVXXyvnazly6iF@fat_crate.local Reported-by: Borislav Petkov Tested-by: Borislav Petkov (AMD) Reported-by: Thomas Gleixner Cc: Vlastimil Babka Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Brendan Jackman Cc: Johannes Weiner Cc: [6.5+] Signed-off-by: Andrew Morton Signed-off-by: Kirill A. Shutemov Signed-off-by: Greg Kroah-Hartman --- mm/page_alloc.c | 27 --------------------------- 1 file changed, 27 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bc62bb2a3b13..74737c35082b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -303,7 +303,6 @@ EXPORT_SYMBOL(nr_online_nodes); static bool page_contains_unaccepted(struct page *page, unsigned int order); static void accept_page(struct page *page, unsigned int order); static bool cond_accept_memory(struct zone *zone, unsigned int order); -static inline bool has_unaccepted_memory(void); static bool __free_unaccepted(struct page *page); int page_group_by_mobility_disabled __read_mostly; @@ -6586,9 +6585,6 @@ bool has_managed_dma(void) #ifdef CONFIG_UNACCEPTED_MEMORY -/* Counts number of zones with unaccepted pages. */ -static DEFINE_STATIC_KEY_FALSE(zones_with_unaccepted_pages); - static bool lazy_accept = true; static int __init accept_memory_parse(char *p) @@ -6624,7 +6620,6 @@ static bool try_to_accept_memory_one(struct zone *zone) { unsigned long flags; struct page *page; - bool last; spin_lock_irqsave(&zone->lock, flags); page = list_first_entry_or_null(&zone->unaccepted_pages, @@ -6635,7 +6630,6 @@ static bool try_to_accept_memory_one(struct zone *zone) } list_del(&page->lru); - last = list_empty(&zone->unaccepted_pages); __mod_zone_freepage_state(zone, -MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE); __mod_zone_page_state(zone, NR_UNACCEPTED, -MAX_ORDER_NR_PAGES); @@ -6645,9 +6639,6 @@ static bool try_to_accept_memory_one(struct zone *zone) __free_pages_ok(page, MAX_ORDER, FPI_TO_TAIL); - if (last) - static_branch_dec(&zones_with_unaccepted_pages); - return true; } @@ -6656,9 +6647,6 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order) long to_accept, wmark; bool ret = false; - if (!has_unaccepted_memory()) - return false; - if (list_empty(&zone->unaccepted_pages)) return false; @@ -6688,30 +6676,20 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order) return ret; } -static inline bool has_unaccepted_memory(void) -{ - return static_branch_unlikely(&zones_with_unaccepted_pages); -} - static bool __free_unaccepted(struct page *page) { struct zone *zone = page_zone(page); unsigned long flags; - bool first = false; if (!lazy_accept) return false; spin_lock_irqsave(&zone->lock, flags); - first = list_empty(&zone->unaccepted_pages); list_add_tail(&page->lru, &zone->unaccepted_pages); __mod_zone_freepage_state(zone, MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE); __mod_zone_page_state(zone, NR_UNACCEPTED, MAX_ORDER_NR_PAGES); spin_unlock_irqrestore(&zone->lock, flags); - if (first) - static_branch_inc(&zones_with_unaccepted_pages); - return true; } @@ -6731,11 +6709,6 @@ static bool cond_accept_memory(struct zone *zone, unsigned int order) return false; } -static inline bool has_unaccepted_memory(void) -{ - return false; -} - static bool __free_unaccepted(struct page *page) { BUILD_BUG();