+ mm-swap-tidy-up-swap-device-and-cluster-info-helpers.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm, swap: tidy up swap device and cluster info helpers
has been added to the -mm mm-unstable branch.  Its filename is
     mm-swap-tidy-up-swap-device-and-cluster-info-helpers.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-tidy-up-swap-device-and-cluster-info-helpers.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm, swap: tidy up swap device and cluster info helpers
Date: Wed, 17 Sep 2025 00:00:52 +0800

swp_swap_info is the most commonly used helper for retrieving swap info. 
It has an internal check that may lead to a NULL return value, but almost
none of its caller checks the return value, making the internal check
pointless.  In fact, most of these callers already ensured the entry is
valid and never expect a NULL value.

Tidy this up and improve the function names.  If the caller can make sure
the swap entry/type is valid and the device is pinned, use the new
introduced __swap_entry_to_info/__swap_type_to_info instead.  They have
more debug sanity checks and lower overhead as they are inlined.

Callers that may expect a NULL value should use
swap_entry_to_info/swap_type_to_info instead.

No feature change.  The rearranged codes should have had no effect, or
they should have been hitting NULL de-ref bugs already.  Only some new
sanity checks are added so potential issues may show up in debug build.

The new helpers will be frequently used with swap table later when working
with swap cache folios.  A locked swap cache folio ensures the entries are
valid and stable so these helpers are very helpful.

Link: https://lkml.kernel.org/r/20250916160100.31545-8-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Suggested-by: Chris Li <chrisl@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/swap.h |    6 ------
 mm/page_io.c         |   12 ++++++------
 mm/swap.h            |   38 +++++++++++++++++++++++++++++++++-----
 mm/swap_state.c      |    4 ++--
 mm/swapfile.c        |   37 +++++++++++++++++++------------------
 5 files changed, 60 insertions(+), 37 deletions(-)

--- a/include/linux/swap.h~mm-swap-tidy-up-swap-device-and-cluster-info-helpers
+++ a/include/linux/swap.h
@@ -479,7 +479,6 @@ extern sector_t swapdev_block(int, pgoff
 extern int __swap_count(swp_entry_t entry);
 extern bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
-struct swap_info_struct *swp_swap_info(swp_entry_t entry);
 struct backing_dev_info;
 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
 extern void exit_swap_address_space(unsigned int type);
@@ -492,11 +491,6 @@ static inline void put_swap_device(struc
 }
 
 #else /* CONFIG_SWAP */
-static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry)
-{
-	return NULL;
-}
-
 static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
 {
 	return NULL;
--- a/mm/page_io.c~mm-swap-tidy-up-swap-device-and-cluster-info-helpers
+++ a/mm/page_io.c
@@ -204,7 +204,7 @@ static bool is_folio_zero_filled(struct
 static void swap_zeromap_folio_set(struct folio *folio)
 {
 	struct obj_cgroup *objcg = get_obj_cgroup_from_folio(folio);
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	int nr_pages = folio_nr_pages(folio);
 	swp_entry_t entry;
 	unsigned int i;
@@ -223,7 +223,7 @@ static void swap_zeromap_folio_set(struc
 
 static void swap_zeromap_folio_clear(struct folio *folio)
 {
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	swp_entry_t entry;
 	unsigned int i;
 
@@ -374,7 +374,7 @@ static void sio_write_complete(struct ki
 static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
 {
 	struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	struct file *swap_file = sis->swap_file;
 	loff_t pos = swap_dev_pos(folio->swap);
 
@@ -446,7 +446,7 @@ static void swap_writepage_bdev_async(st
 
 void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
 {
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 
 	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
 	/*
@@ -537,7 +537,7 @@ static bool swap_read_folio_zeromap(stru
 
 static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 {
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	struct swap_iocb *sio = NULL;
 	loff_t pos = swap_dev_pos(folio->swap);
 
@@ -608,7 +608,7 @@ static void swap_read_folio_bdev_async(s
 
 void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 {
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
 	bool workingset = folio_test_workingset(folio);
 	unsigned long pflags;
--- a/mm/swapfile.c~mm-swap-tidy-up-swap-device-and-cluster-info-helpers
+++ a/mm/swapfile.c
@@ -102,7 +102,7 @@ static PLIST_HEAD(swap_active_head);
 static struct plist_head *swap_avail_heads;
 static DEFINE_SPINLOCK(swap_avail_lock);
 
-static struct swap_info_struct *swap_info[MAX_SWAPFILES];
+struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
@@ -124,14 +124,20 @@ static DEFINE_PER_CPU(struct percpu_swap
 	.lock = INIT_LOCAL_LOCK(),
 };
 
-static struct swap_info_struct *swap_type_to_swap_info(int type)
+/* May return NULL on invalid type, caller must check for NULL return */
+static struct swap_info_struct *swap_type_to_info(int type)
 {
 	if (type >= MAX_SWAPFILES)
 		return NULL;
-
 	return READ_ONCE(swap_info[type]); /* rcu_dereference() */
 }
 
+/* May return NULL on invalid entry, caller must check for NULL return */
+static struct swap_info_struct *swap_entry_to_info(swp_entry_t entry)
+{
+	return swap_type_to_info(swp_type(entry));
+}
+
 static inline unsigned char swap_count(unsigned char ent)
 {
 	return ent & ~SWAP_HAS_CACHE;	/* may include COUNT_CONTINUED flag */
@@ -342,7 +348,7 @@ offset_to_swap_extent(struct swap_info_s
 
 sector_t swap_folio_sector(struct folio *folio)
 {
-	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	struct swap_extent *se;
 	sector_t sector;
 	pgoff_t offset;
@@ -1300,7 +1306,7 @@ static struct swap_info_struct *_swap_in
 
 	if (!entry.val)
 		goto out;
-	si = swp_swap_info(entry);
+	si = swap_entry_to_info(entry);
 	if (!si)
 		goto bad_nofile;
 	if (data_race(!(si->flags & SWP_USED)))
@@ -1415,7 +1421,7 @@ struct swap_info_struct *get_swap_device
 
 	if (!entry.val)
 		goto out;
-	si = swp_swap_info(entry);
+	si = swap_entry_to_info(entry);
 	if (!si)
 		goto bad_nofile;
 	if (!get_swap_device_info(si))
@@ -1538,7 +1544,7 @@ static void swap_entries_free(struct swa
 	unsigned char *map_end = map + nr_pages;
 
 	/* It should never free entries across different clusters */
-	VM_BUG_ON(ci != swp_offset_cluster(si, offset + nr_pages - 1));
+	VM_BUG_ON(ci != __swap_offset_to_cluster(si, offset + nr_pages - 1));
 	VM_BUG_ON(cluster_is_empty(ci));
 	VM_BUG_ON(ci->count < nr_pages);
 
@@ -1596,7 +1602,7 @@ void put_swap_folio(struct folio *folio,
 
 int __swap_count(swp_entry_t entry)
 {
-	struct swap_info_struct *si = swp_swap_info(entry);
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
 	pgoff_t offset = swp_offset(entry);
 
 	return swap_count(si->swap_map[offset]);
@@ -1827,7 +1833,7 @@ out:
 
 swp_entry_t get_swap_page_of_type(int type)
 {
-	struct swap_info_struct *si = swap_type_to_swap_info(type);
+	struct swap_info_struct *si = swap_type_to_info(type);
 	unsigned long offset;
 	swp_entry_t entry = {0};
 
@@ -1908,7 +1914,7 @@ int find_first_swap(dev_t *device)
  */
 sector_t swapdev_block(int type, pgoff_t offset)
 {
-	struct swap_info_struct *si = swap_type_to_swap_info(type);
+	struct swap_info_struct *si = swap_type_to_info(type);
 	struct swap_extent *se;
 
 	if (!si || !(si->flags & SWP_WRITEOK))
@@ -2837,7 +2843,7 @@ static void *swap_start(struct seq_file
 	if (!l)
 		return SEQ_START_TOKEN;
 
-	for (type = 0; (si = swap_type_to_swap_info(type)); type++) {
+	for (type = 0; (si = swap_type_to_info(type)); type++) {
 		if (!(si->flags & SWP_USED) || !si->swap_map)
 			continue;
 		if (!--l)
@@ -2858,7 +2864,7 @@ static void *swap_next(struct seq_file *
 		type = si->type + 1;
 
 	++(*pos);
-	for (; (si = swap_type_to_swap_info(type)); type++) {
+	for (; (si = swap_type_to_info(type)); type++) {
 		if (!(si->flags & SWP_USED) || !si->swap_map)
 			continue;
 		return si;
@@ -3531,7 +3537,7 @@ static int __swap_duplicate(swp_entry_t
 	unsigned char has_cache;
 	int err, i;
 
-	si = swp_swap_info(entry);
+	si = swap_entry_to_info(entry);
 	if (WARN_ON_ONCE(!si)) {
 		pr_err("%s%08lx\n", Bad_file, entry.val);
 		return -EINVAL;
@@ -3646,11 +3652,6 @@ void swapcache_clear(struct swap_info_st
 	swap_entries_put_cache(si, entry, nr);
 }
 
-struct swap_info_struct *swp_swap_info(swp_entry_t entry)
-{
-	return swap_type_to_swap_info(swp_type(entry));
-}
-
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
--- a/mm/swap.h~mm-swap-tidy-up-swap-device-and-cluster-info-helpers
+++ a/mm/swap.h
@@ -15,6 +15,8 @@ extern int page_cluster;
 #define swap_entry_order(order)	0
 #endif
 
+extern struct swap_info_struct *swap_info[];
+
 /*
  * We use this to track usage of a cluster. A cluster is a block of swap disk
  * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
@@ -53,9 +55,29 @@ enum swap_cluster_flags {
 #include <linux/swapops.h> /* for swp_offset */
 #include <linux/blk_types.h> /* for bio_end_io_t */
 
-static inline struct swap_cluster_info *swp_offset_cluster(
+/*
+ * Callers of all helpers below must ensure the entry, type, or offset is
+ * valid, and protect the swap device with reference count or locks.
+ */
+static inline struct swap_info_struct *__swap_type_to_info(int type)
+{
+	struct swap_info_struct *si;
+
+	si = READ_ONCE(swap_info[type]); /* rcu_dereference() */
+	VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
+	return si;
+}
+
+static inline struct swap_info_struct *__swap_entry_to_info(swp_entry_t entry)
+{
+	return __swap_type_to_info(swp_type(entry));
+}
+
+static inline struct swap_cluster_info *__swap_offset_to_cluster(
 		struct swap_info_struct *si, pgoff_t offset)
 {
+	VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
+	VM_WARN_ON_ONCE(offset >= si->max);
 	return &si->cluster_info[offset / SWAPFILE_CLUSTER];
 }
 
@@ -70,8 +92,9 @@ static inline struct swap_cluster_info *
 static inline struct swap_cluster_info *swap_cluster_lock(
 		struct swap_info_struct *si, unsigned long offset)
 {
-	struct swap_cluster_info *ci = swp_offset_cluster(si, offset);
+	struct swap_cluster_info *ci = __swap_offset_to_cluster(si, offset);
 
+	VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
 	spin_lock(&ci->lock);
 	return ci;
 }
@@ -170,7 +193,7 @@ void swap_update_readahead(struct folio
 
 static inline unsigned int folio_swap_flags(struct folio *folio)
 {
-	return swp_swap_info(folio->swap)->flags;
+	return __swap_entry_to_info(folio->swap)->flags;
 }
 
 /*
@@ -181,7 +204,7 @@ static inline unsigned int folio_swap_fl
 static inline int swap_zeromap_batch(swp_entry_t entry, int max_nr,
 		bool *is_zeromap)
 {
-	struct swap_info_struct *sis = swp_swap_info(entry);
+	struct swap_info_struct *sis = __swap_entry_to_info(entry);
 	unsigned long start = swp_offset(entry);
 	unsigned long end = start + max_nr;
 	bool first_bit;
@@ -200,7 +223,7 @@ static inline int swap_zeromap_batch(swp
 
 static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
 {
-	struct swap_info_struct *si = swp_swap_info(entry);
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
 	pgoff_t offset = swp_offset(entry);
 	int i;
 
@@ -219,6 +242,11 @@ static inline int non_swapcache_batch(sw
 
 #else /* CONFIG_SWAP */
 struct swap_iocb;
+static inline struct swap_info_struct *__swap_entry_to_info(swp_entry_t entry)
+{
+	return NULL;
+}
+
 static inline void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 {
 }
--- a/mm/swap_state.c~mm-swap-tidy-up-swap-device-and-cluster-info-helpers
+++ a/mm/swap_state.c
@@ -336,7 +336,7 @@ struct folio *__read_swap_cache_async(sw
 		struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
 		bool skip_if_exists)
 {
-	struct swap_info_struct *si = swp_swap_info(entry);
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
 	struct folio *folio;
 	struct folio *new_folio = NULL;
 	struct folio *result = NULL;
@@ -560,7 +560,7 @@ struct folio *swap_cluster_readahead(swp
 	unsigned long offset = entry_offset;
 	unsigned long start_offset, end_offset;
 	unsigned long mask;
-	struct swap_info_struct *si = swp_swap_info(entry);
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
 	struct blk_plug plug;
 	struct swap_iocb *splug = NULL;
 	bool page_allocated;
_

Patches currently in -mm which might be from kasong@tencent.com are

mm-swap-use-unified-helper-for-swap-cache-look-up.patch
mm-swap-fix-swap-cache-index-error-when-retrying-reclaim.patch
mm-swap-check-page-poison-flag-after-locking-it.patch
mm-swap-always-lock-and-check-the-swap-cache-folio-before-use.patch
mm-swap-rename-and-move-some-swap-cluster-definition-and-helpers.patch
mm-swap-tidy-up-swap-device-and-cluster-info-helpers.patch
mm-swap-cleanup-swap-cache-api-and-add-kerneldoc.patch
mm-shmem-swap-remove-redundant-error-handling-for-replacing-folio.patch
mm-swap-wrap-swap-cache-replacement-with-a-helper.patch
mm-swap-use-the-swap-table-for-the-swap-cache-and-switch-api.patch
mm-swap-mark-swap-address-space-ro-and-add-context-debug-check.patch
mm-swap-remove-contention-workaround-for-swap-cache.patch
mm-swap-implement-dynamic-allocation-of-swap-table.patch
mm-swap-use-a-single-page-for-swap-table-when-the-size-fits.patch