[PATCH 6.18 706/752] mm/page_alloc: skip debug_check_no_{obj,locks}_freed with FPI_TRYLOCK

Sasha Levin
2026-02-28T17:58:41Z

From: Harry Yoo <harry.yoo@oracle.com>

[ Upstream commit 338ad1e84d15078a9ae46d7dd7466329ae0bfa61 ]

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.

Link: https://lkml.kernel.org/r/20260209062639.16577-1-harry.yoo@oracle.com
Fixes: 8c57b687e833 ("mm, bpf: Introduce free_pages_nolock()")
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 10708f37575d4..f44524e1c92ac 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1339,8 +1339,8 @@ 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);
@@ -1433,7 +1433,7 @@ __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),
@@ -1472,6 +1472,11 @@ __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.
@@ -1605,7 +1610,7 @@ 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);
}

@@ -2931,7 +2936,7 @@ 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;

/*
@@ -2988,7 +2993,7 @@ 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
--
2.51.0