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* [PATCH V2] mm/page_alloc: skip debug_check_no_{obj,locks}_freed with FPI_TRYLOCK
@ 2026-02-09  6:26 Harry Yoo
  2026-02-09 10:51 ` Vlastimil Babka
  2026-02-09 16:37 ` Zi Yan
  0 siblings, 2 replies; 3+ messages in thread
From: Harry Yoo @ 2026-02-09  6:26 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Vlastimil Babka, Suren Baghdasaryan, Michal Hocko,
	Brendan Jackman, Johannes Weiner, Zi Yan, Alexei Starovoitov,
	Sebastian Andrzej Siewior, Shakeel Butt, linux-mm, Harry Yoo,
	stable

When CONFIG_DEBUG_OBJECTS_FREE is enabled,
debug_check_no_{obj,locks}_freed() functions are called.

Since both of them spin on a lock, they are not safe to be called
if the FPI_TRYLOCK flag is specified. This leads to a lockdep splat:

  ================================
  WARNING: inconsistent lock state
  6.19.0-rc5-slab-for-next+ #326 Tainted: G                 N
  --------------------------------
  inconsistent {INITIAL USE} -> {IN-NMI} usage.
  kunit_try_catch/9046 [HC2[2]:SC0[0]:HE0:SE1] takes:
  ffffffff84ed6bf8 (&obj_hash[i].lock){-.-.}-{2:2}, at: __debug_check_no_obj_freed+0xe0/0x300
  {INITIAL USE} state was registered at:
    lock_acquire+0xd9/0x2f0
    _raw_spin_lock_irqsave+0x4c/0x80
    __debug_object_init+0x9d/0x1f0
    debug_object_init+0x34/0x50
    __init_work+0x28/0x40
    init_cgroup_housekeeping+0x151/0x210
    init_cgroup_root+0x3d/0x140
    cgroup_init_early+0x30/0x240
    start_kernel+0x3e/0xcd0
    x86_64_start_reservations+0x18/0x30
    x86_64_start_kernel+0xf3/0x140
    common_startup_64+0x13e/0x148
  irq event stamp: 2998
  hardirqs last  enabled at (2997): [<ffffffff8298b77a>] exc_nmi+0x11a/0x240
  hardirqs last disabled at (2998): [<ffffffff8298b991>] sysvec_irq_work+0x11/0x110
  softirqs last  enabled at (1416): [<ffffffff813c1f72>] __irq_exit_rcu+0x132/0x1c0
  softirqs last disabled at (1303): [<ffffffff813c1f72>] __irq_exit_rcu+0x132/0x1c0

  other info that might help us debug this:
   Possible unsafe locking scenario:

         CPU0
         ----
    lock(&obj_hash[i].lock);
    <Interrupt>
      lock(&obj_hash[i].lock);

   *** DEADLOCK ***

Rename free_pages_prepare() to __free_pages_prepare(), add an fpi_t
parameter, and skip those checks if FPI_TRYLOCK is set. To keep the
fpi_t definition in mm/page_alloc.c, add a wrapper function
free_pages_prepare() that always passes FPI_NONE and use it in
mm/compaction.c.

Fixes: 8c57b687e833 ("mm, bpf: Introduce free_pages_nolock()")
Cc: <stable@vger.kernel.org>
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
---

V1 -> v2:

  Per Vlastimil's suggestion, rename free_pages_prepare() to
  __free_pages_prepare() instead of moving the fpi_t definition to
  mm/internal.h. __free_pages_prepare() takes fpi_t as parameter,
  free_pages_prepare() always passes FPI_NONE to __free_pages_prepare().

 mm/page_alloc.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cbf758e27aa2..1513084d7507 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1340,8 +1340,8 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
-__always_inline bool free_pages_prepare(struct page *page,
-			unsigned int order)
+__always_inline bool __free_pages_prepare(struct page *page,
+					  unsigned int order, fpi_t fpi_flags)
 {
 	int bad = 0;
 	bool skip_kasan_poison = should_skip_kasan_poison(page);
@@ -1434,7 +1434,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 	page_table_check_free(page, order);
 	pgalloc_tag_sub(page, 1 << order);
 
-	if (!PageHighMem(page)) {
+	if (!PageHighMem(page) && !(fpi_flags & FPI_TRYLOCK)) {
 		debug_check_no_locks_freed(page_address(page),
 					   PAGE_SIZE << order);
 		debug_check_no_obj_freed(page_address(page),
@@ -1473,6 +1473,11 @@ __always_inline bool free_pages_prepare(struct page *page,
 	return true;
 }
 
+bool free_pages_prepare(struct page *page, unsigned int order)
+{
+	return __free_pages_prepare(page, order, FPI_NONE);
+}
+
 /*
  * Frees a number of pages from the PCP lists
  * Assumes all pages on list are in same zone.
@@ -1606,7 +1611,7 @@ static void __free_pages_ok(struct page *page, unsigned int order,
 	unsigned long pfn = page_to_pfn(page);
 	struct zone *zone = page_zone(page);
 
-	if (free_pages_prepare(page, order))
+	if (__free_pages_prepare(page, order, fpi_flags))
 		free_one_page(zone, page, pfn, order, fpi_flags);
 }
 
@@ -2970,7 +2975,7 @@ static void __free_frozen_pages(struct page *page, unsigned int order,
 		return;
 	}
 
-	if (!free_pages_prepare(page, order))
+	if (!__free_pages_prepare(page, order, fpi_flags))
 		return;
 
 	/*
@@ -3027,7 +3032,7 @@ void free_unref_folios(struct folio_batch *folios)
 		unsigned long pfn = folio_pfn(folio);
 		unsigned int order = folio_order(folio);
 
-		if (!free_pages_prepare(&folio->page, order))
+		if (!__free_pages_prepare(&folio->page, order, FPI_NONE))
 			continue;
 		/*
 		 * Free orders not handled on the PCP directly to the
-- 
2.43.0



^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-02-09 16:38 UTC | newest]

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2026-02-09  6:26 [PATCH V2] mm/page_alloc: skip debug_check_no_{obj,locks}_freed with FPI_TRYLOCK Harry Yoo
2026-02-09 10:51 ` Vlastimil Babka
2026-02-09 16:37 ` Zi Yan

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