[PATCH v17 25/47] dept: track PG_locked with dept

Byungchul Park
2025-10-02T08:13:54Z

Makes dept able to track PG_locked waits and events, which will be
useful in practice. See the following link that shows dept worked with
PG_locked and detected real issues in practice:

https://lore.kernel.org/lkml/1674268856-31807-1-git-send-email-byungchul.park@lge.com/

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
include/linux/mm_types.h | 2 +
include/linux/page-flags.h | 125 +++++++++++++++++++++++++++++++++----
include/linux/pagemap.h | 37 ++++++++++-
mm/filemap.c | 26 ++++++++
mm/mm_init.c | 2 +
5 files changed, 179 insertions(+), 13 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index a643fae8a349..5ebc565309af 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -20,6 +20,7 @@
#include <linux/seqlock.h>
#include <linux/percpu_counter.h>
#include <linux/types.h>
+#include <linux/dept.h>

#include <asm/mmu.h>

@@ -223,6 +224,7 @@ struct page {
struct page *kmsan_shadow;
struct page *kmsan_origin;
#endif
+ struct dept_ext_wgen pg_locked_wgen;
} _struct_page_alignment;

/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 8d3fa3a91ce4..d3c4954c4218 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -198,6 +198,61 @@ enum pageflags {

#ifndef __GENERATING_BOUNDS_H

+#ifdef CONFIG_DEPT
+#include <linux/kernel.h>
+#include <linux/dept.h>
+
+extern struct dept_map pg_locked_map;
+
+/*
+ * Place the following annotations in its suitable point in code:
+ *
+ * Annotate dept_page_set_bit() around firstly set_bit*()
+ * Annotate dept_page_clear_bit() around clear_bit*()
+ * Annotate dept_page_wait_on_bit() around wait_on_bit*()
+ */
+
+static inline void dept_page_set_bit(struct page *p, int bit_nr)
+{
+ if (bit_nr == PG_locked)
+ dept_request_event(&pg_locked_map, &p->pg_locked_wgen);
+}
+
+static inline void dept_page_clear_bit(struct page *p, int bit_nr)
+{
+ if (bit_nr == PG_locked)
+ dept_event(&pg_locked_map, 1UL, _RET_IP_, __func__, &p->pg_locked_wgen);
+}
+
+static inline void dept_page_wait_on_bit(struct page *p, int bit_nr)
+{
+ if (bit_nr == PG_locked)
+ dept_wait(&pg_locked_map, 1UL, _RET_IP_, __func__, 0, -1L);
+}
+
+static inline void dept_folio_set_bit(struct folio *f, int bit_nr)
+{
+ dept_page_set_bit(&f->page, bit_nr);
+}
+
+static inline void dept_folio_clear_bit(struct folio *f, int bit_nr)
+{
+ dept_page_clear_bit(&f->page, bit_nr);
+}
+
+static inline void dept_folio_wait_on_bit(struct folio *f, int bit_nr)
+{
+ dept_page_wait_on_bit(&f->page, bit_nr);
+}
+#else
+#define dept_page_set_bit(p, bit_nr) do { } while (0)
+#define dept_page_clear_bit(p, bit_nr) do { } while (0)
+#define dept_page_wait_on_bit(p, bit_nr) do { } while (0)
+#define dept_folio_set_bit(f, bit_nr) do { } while (0)
+#define dept_folio_clear_bit(f, bit_nr) do { } while (0)
+#define dept_folio_wait_on_bit(f, bit_nr) do { } while (0)
+#endif
+
#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
DECLARE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);

@@ -419,27 +474,51 @@ static __always_inline bool folio_test_##name(const struct folio *folio) \

#define FOLIO_SET_FLAG(name, page) \
static __always_inline void folio_set_##name(struct folio *folio) \
-{ set_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ set_bit(PG_##name, folio_flags(folio, page)); \
+ dept_folio_set_bit(folio, PG_##name); \
+}

#define FOLIO_CLEAR_FLAG(name, page) \
static __always_inline void folio_clear_##name(struct folio *folio) \
-{ clear_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ clear_bit(PG_##name, folio_flags(folio, page)); \
+ dept_folio_clear_bit(folio, PG_##name); \
+}

#define __FOLIO_SET_FLAG(name, page) \
static __always_inline void __folio_set_##name(struct folio *folio) \
-{ __set_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ __set_bit(PG_##name, folio_flags(folio, page)); \
+ dept_folio_set_bit(folio, PG_##name); \
+}

#define __FOLIO_CLEAR_FLAG(name, page) \
static __always_inline void __folio_clear_##name(struct folio *folio) \
-{ __clear_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ __clear_bit(PG_##name, folio_flags(folio, page)); \
+ dept_folio_clear_bit(folio, PG_##name); \
+}

#define FOLIO_TEST_SET_FLAG(name, page) \
static __always_inline bool folio_test_set_##name(struct folio *folio) \
-{ return test_and_set_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ bool __ret = test_and_set_bit(PG_##name, folio_flags(folio, page)); \
+ \
+ if (!__ret) \
+ dept_folio_set_bit(folio, PG_##name); \
+ return __ret; \
+}

#define FOLIO_TEST_CLEAR_FLAG(name, page) \
static __always_inline bool folio_test_clear_##name(struct folio *folio) \
-{ return test_and_clear_bit(PG_##name, folio_flags(folio, page)); }
+{ \
+ bool __ret = test_and_clear_bit(PG_##name, folio_flags(folio, page)); \
+ \
+ if (__ret) \
+ dept_folio_clear_bit(folio, PG_##name); \
+ return __ret; \
+}

#define FOLIO_FLAG(name, page) \
FOLIO_TEST_FLAG(name, page) \
@@ -454,32 +533,54 @@ static __always_inline int Page##uname(const struct page *page) \
#define SETPAGEFLAG(uname, lname, policy) \
FOLIO_SET_FLAG(lname, FOLIO_##policy) \
static __always_inline void SetPage##uname(struct page *page) \
-{ set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ set_bit(PG_##lname, &policy(page, 1)->flags); \
+ dept_page_set_bit(page, PG_##lname); \
+}

#define CLEARPAGEFLAG(uname, lname, policy) \
FOLIO_CLEAR_FLAG(lname, FOLIO_##policy) \
static __always_inline void ClearPage##uname(struct page *page) \
-{ clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ clear_bit(PG_##lname, &policy(page, 1)->flags); \
+ dept_page_clear_bit(page, PG_##lname); \
+}

#define __SETPAGEFLAG(uname, lname, policy) \
__FOLIO_SET_FLAG(lname, FOLIO_##policy) \
static __always_inline void __SetPage##uname(struct page *page) \
-{ __set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ __set_bit(PG_##lname, &policy(page, 1)->flags); \
+ dept_page_set_bit(page, PG_##lname); \
+}

#define __CLEARPAGEFLAG(uname, lname, policy) \
__FOLIO_CLEAR_FLAG(lname, FOLIO_##policy) \
static __always_inline void __ClearPage##uname(struct page *page) \
-{ __clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ __clear_bit(PG_##lname, &policy(page, 1)->flags); \
+ dept_page_clear_bit(page, PG_##lname); \
+}

#define TESTSETFLAG(uname, lname, policy) \
FOLIO_TEST_SET_FLAG(lname, FOLIO_##policy) \
static __always_inline int TestSetPage##uname(struct page *page) \
-{ return test_and_set_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ bool ret = test_and_set_bit(PG_##lname, &policy(page, 1)->flags);\
+ if (!ret) \
+ dept_page_set_bit(page, PG_##lname); \
+ return ret; \
+}

#define TESTCLEARFLAG(uname, lname, policy) \
FOLIO_TEST_CLEAR_FLAG(lname, FOLIO_##policy) \
static __always_inline int TestClearPage##uname(struct page *page) \
-{ return test_and_clear_bit(PG_##lname, &policy(page, 1)->flags); }
+{ \
+ bool ret = test_and_clear_bit(PG_##lname, &policy(page, 1)->flags);\
+ if (ret) \
+ dept_page_clear_bit(page, PG_##lname); \
+ return ret; \
+}

#define PAGEFLAG(uname, lname, policy) \
TESTPAGEFLAG(uname, lname, policy) \
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 12a12dae727d..53b68b7a3f17 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1093,7 +1093,12 @@ void folio_unlock(struct folio *folio);
*/
static inline bool folio_trylock(struct folio *folio)
{
- return likely(!test_and_set_bit_lock(PG_locked, folio_flags(folio, 0)));
+ bool ret = !test_and_set_bit_lock(PG_locked, folio_flags(folio, 0));
+
+ if (ret)
+ dept_page_set_bit(&folio->page, PG_locked);
+
+ return likely(ret);
}

/*
@@ -1129,6 +1134,16 @@ static inline bool trylock_page(struct page *page)
static inline void folio_lock(struct folio *folio)
{
might_sleep();
+
+ /*
+ * dept_page_wait_on_bit() will be called if __folio_lock() goes
+ * through a real wait path. However, for better job to detect
+ * *potential* deadlocks, let's assume that folio_lock() always
+ * goes through wait so that dept can take into account all the
+ * potential cases.
+ */
+ dept_page_wait_on_bit(&folio->page, PG_locked);
+
if (!folio_trylock(folio))
__folio_lock(folio);
}
@@ -1149,6 +1164,15 @@ static inline void lock_page(struct page *page)
struct folio *folio;
might_sleep();

+ /*
+ * dept_page_wait_on_bit() will be called if __folio_lock() goes
+ * through a real wait path. However, for better job to detect
+ * *potential* deadlocks, let's assume that lock_page() always
+ * goes through wait so that dept can take into account all the
+ * potential cases.
+ */
+ dept_page_wait_on_bit(page, PG_locked);
+
folio = page_folio(page);
if (!folio_trylock(folio))
__folio_lock(folio);
@@ -1167,6 +1191,17 @@ static inline void lock_page(struct page *page)
static inline int folio_lock_killable(struct folio *folio)
{
might_sleep();
+
+ /*
+ * dept_page_wait_on_bit() will be called if
+ * __folio_lock_killable() goes through a real wait path.
+ * However, for better job to detect *potential* deadlocks,
+ * let's assume that folio_lock_killable() always goes through
+ * wait so that dept can take into account all the potential
+ * cases.
+ */
+ dept_page_wait_on_bit(&folio->page, PG_locked);
+
if (!folio_trylock(folio))
return __folio_lock_killable(folio);
return 0;
diff --git a/mm/filemap.c b/mm/filemap.c
index 751838ef05e5..edb0710ddb3f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -48,6 +48,7 @@
#include <linux/rcupdate_wait.h>
#include <linux/sched/mm.h>
#include <linux/sysctl.h>
+#include <linux/dept.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "internal.h"
@@ -1145,6 +1146,7 @@ static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync,
if (flags & WQ_FLAG_CUSTOM) {
if (test_and_set_bit(key->bit_nr, &key->folio->flags))
return -1;
+ dept_page_set_bit(&key->folio->page, key->bit_nr);
flags |= WQ_FLAG_DONE;
}
}
@@ -1228,6 +1230,7 @@ static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
if (wait->flags & WQ_FLAG_EXCLUSIVE) {
if (test_and_set_bit(bit_nr, &folio->flags))
return false;
+ dept_page_set_bit(&folio->page, bit_nr);
} else if (test_bit(bit_nr, &folio->flags))
return false;

@@ -1235,6 +1238,9 @@ static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
return true;
}

+struct dept_map __maybe_unused pg_locked_map = DEPT_MAP_INITIALIZER(pg_locked_map, NULL);
+EXPORT_SYMBOL(pg_locked_map);
+
static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
int state, enum behavior behavior)
{
@@ -1246,6 +1252,8 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
unsigned long pflags;
bool in_thrashing;

+ dept_page_wait_on_bit(&folio->page, bit_nr);
+
if (bit_nr == PG_locked &&
!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
delayacct_thrashing_start(&in_thrashing);
@@ -1339,6 +1347,23 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
break;
}

+ /*
+ * dept_page_set_bit() might have been called already in
+ * folio_trylock_flag(), wake_page_function() or somewhere.
+ * However, call it again to reset the wgen of dept to ensure
+ * dept_page_wait_on_bit() is called prior to
+ * dept_page_set_bit().
+ *
+ * Remind dept considers all the waits between
+ * dept_page_set_bit() and dept_page_clear_bit() as potential
+ * event disturbers. Ensure the correct sequence so that dept
+ * can make correct decisions:
+ *
+ * wait -> acquire(set bit) -> release(clear bit)
+ */
+ if (wait->flags & WQ_FLAG_DONE)
+ dept_page_set_bit(&folio->page, bit_nr);
+
/*
* If a signal happened, this 'finish_wait()' may remove the last
* waiter from the wait-queues, but the folio waiters bit will remain
@@ -1496,6 +1521,7 @@ void folio_unlock(struct folio *folio)
BUILD_BUG_ON(PG_waiters != 7);
BUILD_BUG_ON(PG_locked > 7);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+ dept_page_clear_bit(&folio->page, PG_locked);
if (folio_xor_flags_has_waiters(folio, 1 << PG_locked))
folio_wake_bit(folio, PG_locked);
}
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 5c21b3af216b..09e4ac6a73c7 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -32,6 +32,7 @@
#include <linux/vmstat.h>
#include <linux/kexec_handover.h>
#include <linux/hugetlb.h>
+#include <linux/dept.h>
#include "internal.h"
#include "slab.h"
#include "shuffle.h"
@@ -587,6 +588,7 @@ void __meminit __init_single_page(struct page *page, unsigned long pfn,
atomic_set(&page->_mapcount, -1);
page_cpupid_reset_last(page);
page_kasan_tag_reset(page);
+ dept_ext_wgen_init(&page->pg_locked_wgen);

INIT_LIST_HEAD(&page->lru);
#ifdef WANT_PAGE_VIRTUAL
--
2.17.1