[merged mm-stable] mm-swap-clean-up-swapon-process-and-locking.patch removed from -mm tree

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

The quilt patch titled
     Subject: mm, swap: clean up swapon process and locking
has been removed from the -mm tree.  Its filename was
     mm-swap-clean-up-swapon-process-and-locking.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm, swap: clean up swapon process and locking
Date: Wed, 18 Feb 2026 04:06:27 +0800

Slightly clean up the swapon process.  Add comments about what swap_lock
protects, introduce and rename helpers that wrap swap_map and cluster_info
setup, and do it outside of the swap_lock lock.

This lock protection is not needed for swap_map and cluster_info setup
because all swap users must either hold the percpu ref or hold a stable
allocated swap entry (e.g., locking a folio in the swap cache) before
accessing.  So before the swap device is exposed by enable_swap_info,
nothing would use the swap device's map or cluster.

So we are safe to allocate and set up swap data freely first, then expose
the swap device and set the SWP_WRITEOK flag.

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-2-f4e34be021a7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/swapfile.c |   87 ++++++++++++++++++++++++++----------------------
 1 file changed, 48 insertions(+), 39 deletions(-)

--- a/mm/swapfile.c~mm-swap-clean-up-swapon-process-and-locking
+++ a/mm/swapfile.c
@@ -65,6 +65,13 @@ static void move_cluster(struct swap_inf
 			 struct swap_cluster_info *ci, struct list_head *list,
 			 enum swap_cluster_flags new_flags);
 
+/*
+ * Protects the swap_info array, and the SWP_USED flag. swap_info contains
+ * lazily allocated & freed swap device info struts, and SWP_USED indicates
+ * which device is used, ~SWP_USED devices and can be reused.
+ *
+ * Also protects swap_active_head total_swap_pages, and the SWP_WRITEOK flag.
+ */
 static DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 atomic_long_t nr_swap_pages;
@@ -2657,8 +2664,6 @@ static int setup_swap_extents(struct swa
 }
 
 static void setup_swap_info(struct swap_info_struct *si, int prio,
-			    unsigned char *swap_map,
-			    struct swap_cluster_info *cluster_info,
 			    unsigned long *zeromap)
 {
 	si->prio = prio;
@@ -2668,8 +2673,6 @@ static void setup_swap_info(struct swap_
 	 */
 	si->list.prio = -si->prio;
 	si->avail_list.prio = -si->prio;
-	si->swap_map = swap_map;
-	si->cluster_info = cluster_info;
 	si->zeromap = zeromap;
 }
 
@@ -2687,13 +2690,11 @@ static void _enable_swap_info(struct swa
 }
 
 static void enable_swap_info(struct swap_info_struct *si, int prio,
-				unsigned char *swap_map,
-				struct swap_cluster_info *cluster_info,
-				unsigned long *zeromap)
+			     unsigned long *zeromap)
 {
 	spin_lock(&swap_lock);
 	spin_lock(&si->lock);
-	setup_swap_info(si, prio, swap_map, cluster_info, zeromap);
+	setup_swap_info(si, prio, zeromap);
 	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
 	/*
@@ -2711,7 +2712,7 @@ static void reinsert_swap_info(struct sw
 {
 	spin_lock(&swap_lock);
 	spin_lock(&si->lock);
-	setup_swap_info(si, si->prio, si->swap_map, si->cluster_info, si->zeromap);
+	setup_swap_info(si, si->prio, si->zeromap);
 	_enable_swap_info(si);
 	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
@@ -2735,8 +2736,8 @@ static void wait_for_allocation(struct s
 	}
 }
 
-static void free_cluster_info(struct swap_cluster_info *cluster_info,
-			      unsigned long maxpages)
+static void free_swap_cluster_info(struct swap_cluster_info *cluster_info,
+				   unsigned long maxpages)
 {
 	struct swap_cluster_info *ci;
 	int i, nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
@@ -2889,7 +2890,7 @@ SYSCALL_DEFINE1(swapoff, const char __us
 	p->global_cluster = NULL;
 	vfree(swap_map);
 	kvfree(zeromap);
-	free_cluster_info(cluster_info, maxpages);
+	free_swap_cluster_info(cluster_info, maxpages);
 	/* Destroy swap account information */
 	swap_cgroup_swapoff(p->type);
 
@@ -3236,10 +3237,15 @@ static unsigned long read_swap_header(st
 
 static int setup_swap_map(struct swap_info_struct *si,
 			  union swap_header *swap_header,
-			  unsigned char *swap_map,
 			  unsigned long maxpages)
 {
 	unsigned long i;
+	unsigned char *swap_map;
+
+	swap_map = vzalloc(maxpages);
+	si->swap_map = swap_map;
+	if (!swap_map)
+		return -ENOMEM;
 
 	swap_map[0] = SWAP_MAP_BAD; /* omit header page */
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
@@ -3260,9 +3266,9 @@ static int setup_swap_map(struct swap_in
 	return 0;
 }
 
-static struct swap_cluster_info *setup_clusters(struct swap_info_struct *si,
-						union swap_header *swap_header,
-						unsigned long maxpages)
+static int setup_swap_clusters_info(struct swap_info_struct *si,
+				    union swap_header *swap_header,
+				    unsigned long maxpages)
 {
 	unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
 	struct swap_cluster_info *cluster_info;
@@ -3331,10 +3337,11 @@ static struct swap_cluster_info *setup_c
 		}
 	}
 
-	return cluster_info;
+	si->cluster_info = cluster_info;
+	return 0;
 err:
-	free_cluster_info(cluster_info, maxpages);
-	return ERR_PTR(err);
+	free_swap_cluster_info(cluster_info, maxpages);
+	return err;
 }
 
 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
@@ -3349,9 +3356,7 @@ SYSCALL_DEFINE2(swapon, const char __use
 	int nr_extents;
 	sector_t span;
 	unsigned long maxpages;
-	unsigned char *swap_map = NULL;
 	unsigned long *zeromap = NULL;
-	struct swap_cluster_info *cluster_info = NULL;
 	struct folio *folio = NULL;
 	struct inode *inode = NULL;
 	bool inced_nr_rotate_swap = false;
@@ -3362,6 +3367,11 @@ SYSCALL_DEFINE2(swapon, const char __use
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	/*
+	 * Allocate or reuse existing !SWP_USED swap_info. The returned
+	 * si will stay in a dying status, so nothing will access its content
+	 * until enable_swap_info resurrects its percpu ref and expose it.
+	 */
 	si = alloc_swap_info();
 	if (IS_ERR(si))
 		return PTR_ERR(si);
@@ -3439,18 +3449,17 @@ SYSCALL_DEFINE2(swapon, const char __use
 
 	maxpages = si->max;
 
-	/* OK, set up the swap map and apply the bad block list */
-	swap_map = vzalloc(maxpages);
-	if (!swap_map) {
-		error = -ENOMEM;
+	/* Setup the swap map and apply bad block */
+	error = setup_swap_map(si, swap_header, maxpages);
+	if (error)
 		goto bad_swap_unlock_inode;
-	}
 
-	error = swap_cgroup_swapon(si->type, maxpages);
+	/* Set up the swap cluster info */
+	error = setup_swap_clusters_info(si, swap_header, maxpages);
 	if (error)
 		goto bad_swap_unlock_inode;
 
-	error = setup_swap_map(si, swap_header, swap_map, maxpages);
+	error = swap_cgroup_swapon(si->type, maxpages);
 	if (error)
 		goto bad_swap_unlock_inode;
 
@@ -3478,13 +3487,6 @@ SYSCALL_DEFINE2(swapon, const char __use
 		inced_nr_rotate_swap = true;
 	}
 
-	cluster_info = setup_clusters(si, swap_header, maxpages);
-	if (IS_ERR(cluster_info)) {
-		error = PTR_ERR(cluster_info);
-		cluster_info = NULL;
-		goto bad_swap_unlock_inode;
-	}
-
 	if ((swap_flags & SWAP_FLAG_DISCARD) &&
 	    si->bdev && bdev_max_discard_sectors(si->bdev)) {
 		/*
@@ -3537,7 +3539,9 @@ SYSCALL_DEFINE2(swapon, const char __use
 		prio = swap_flags & SWAP_FLAG_PRIO_MASK;
 
 	si->swap_file = swap_file;
-	enable_swap_info(si, prio, swap_map, cluster_info, zeromap);
+
+	/* Sets SWP_WRITEOK, resurrect the percpu ref, expose the swap device */
+	enable_swap_info(si, prio, zeromap);
 
 	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
 		K(si->pages), name->name, si->prio, nr_extents,
@@ -3563,13 +3567,18 @@ bad_swap:
 	inode = NULL;
 	destroy_swap_extents(si, swap_file);
 	swap_cgroup_swapoff(si->type);
+	vfree(si->swap_map);
+	si->swap_map = NULL;
+	free_swap_cluster_info(si->cluster_info, si->max);
+	si->cluster_info = NULL;
+	/*
+	 * Clear the SWP_USED flag after all resources are freed so
+	 * alloc_swap_info can reuse this si safely.
+	 */
 	spin_lock(&swap_lock);
 	si->flags = 0;
 	spin_unlock(&swap_lock);
-	vfree(swap_map);
 	kvfree(zeromap);
-	if (cluster_info)
-		free_cluster_info(cluster_info, maxpages);
 	if (inced_nr_rotate_swap)
 		atomic_dec(&nr_rotate_swap);
 	if (swap_file)
_

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