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Message-ID: <20250506112509.905147-3-kirill.shutemov@linux.intel.com>
Date: Tue, 6 May 2025 14:25:09 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: akpm@...ux-foundation.org,
vbabka@...e.cz,
surenb@...gle.com,
mhocko@...e.com,
jackmanb@...gle.com,
hannes@...xchg.org,
bp@...en8.de,
tglx@...utronix.de,
david@...hat.com
Cc: ast@...nel.org,
linux-mm@...ck.org,
linux-coco@...ts.linux.dev,
linux-kernel@...r.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
stable@...r.kernel.org
Subject: [PATCH 2/2] mm/page_alloc: Fix race condition in unaccepted memory handling
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.
Borisal 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.
The effect of this static_branch optimization is only visible on
microbenchmark.
Instead of adding more complexity around it, remove it altogether.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory")
Link: https://lore.kernel.org/all/20250506092445.GBaBnVXXyvnazly6iF@fat_crate.local
Reported-by: Borislav Petkov <bp@...en8.de>
Reported-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org # v6.5+
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Brendan Jackman <jackmanb@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>
---
mm/internal.h | 1 -
mm/mm_init.c | 1 -
mm/page_alloc.c | 47 -----------------------------------------------
3 files changed, 49 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index e9695baa5922..50c2f590b2d0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1595,7 +1595,6 @@ 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)
{
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 9659689b8ace..84f14fa12d0d 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1441,7 +1441,6 @@ 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
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5fccf5fce084..a4a4df2daedb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7175,16 +7175,8 @@ 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;
-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")) {
@@ -7209,11 +7201,7 @@ static bool page_contains_unaccepted(struct page *page, unsigned int order)
static void __accept_page(struct zone *zone, unsigned long *flags,
struct page *page)
{
- bool last;
-
list_del(&page->lru);
- last = list_empty(&zone->unaccepted_pages);
-
account_freepages(zone, -MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE);
__mod_zone_page_state(zone, NR_UNACCEPTED, -MAX_ORDER_NR_PAGES);
__ClearPageUnaccepted(page);
@@ -7222,28 +7210,6 @@ static void __accept_page(struct zone *zone, unsigned long *flags,
accept_memory(page_to_phys(page), PAGE_SIZE << MAX_PAGE_ORDER);
__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);
- }
}
void accept_page(struct page *page)
@@ -7280,20 +7246,12 @@ static bool try_to_accept_memory_one(struct zone *zone)
return true;
}
-static inline bool has_unaccepted_memory(void)
-{
- return static_branch_unlikely(&zones_with_unaccepted_pages);
-}
-
static bool cond_accept_memory(struct zone *zone, unsigned int order,
int alloc_flags)
{
long to_accept, wmark;
bool ret = false;
- if (!has_unaccepted_memory())
- return false;
-
if (list_empty(&zone->unaccepted_pages))
return false;
@@ -7331,22 +7289,17 @@ 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);
account_freepages(zone, MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE);
__mod_zone_page_state(zone, NR_UNACCEPTED, MAX_ORDER_NR_PAGES);
__SetPageUnaccepted(page);
spin_unlock_irqrestore(&zone->lock, flags);
- if (first)
- static_branch_inc(&zones_with_unaccepted_pages);
-
return true;
}
--
2.47.2
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