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Message-Id: <20260126-swap-table-p3-v1-1-a74155fab9b0@tencent.com>
Date: Mon, 26 Jan 2026 01:57:24 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Kemeng Shi <shikemeng@...weicloud.com>, Nhat Pham <nphamcs@...il.com>,
Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, David Hildenbrand <david@...nel.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, linux-kernel@...r.kernel.org,
Chris Li <chrisl@...nel.org>, Kairui Song <kasong@...cent.com>
Subject: [PATCH 01/12] mm, swap: protect si->swap_file properly and use as
a mount indicator
From: Kairui Song <kasong@...cent.com>
/proc/swaps uses si->swap_map as the indicator to check if the swap
device is mounted. swap_map will be removed soon, so change it to use
si->swap_file instead because:
- si->swap_file is exactly the only dynamic content that /proc/swaps is
interested in. Previously, it was checking si->swap_map just to ensure
si->swap_file is available. si->swap_map is set under mutex
protection, and after si->swap_file is set, so having si->swap_map set
guarantees si->swap_file is set.
- Checking si->flags doesn't work here. SWP_WRITEOK is cleared during
swapoff, but /proc/swaps is supposed to show the device under swapoff
too to report the swapoff progress. And SWP_USED is set even if the
device hasn't been properly set up.
We can have another flag, but the easier way is to just check
si->swap_file directly. So protect si->swap_file setting with mutext,
and set si->swap_file only when the swap device is truly enabled.
/proc/swaps only interested in si->swap_file and a few static data
reading. Only si->swap_file needs protection. Reading other static
fields is always fine.
Signed-off-by: Kairui Song <kasong@...cent.com>
---
mm/swapfile.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7b055f15d705..521f7713a7c3 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -110,6 +110,7 @@ struct swap_info_struct *swap_info[MAX_SWAPFILES];
static struct kmem_cache *swap_table_cachep;
+/* Protects si->swap_file for /proc/swaps usage */
static DEFINE_MUTEX(swapon_mutex);
static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
@@ -2521,7 +2522,8 @@ static void drain_mmlist(void)
/*
* Free all of a swapdev's extent information
*/
-static void destroy_swap_extents(struct swap_info_struct *sis)
+static void destroy_swap_extents(struct swap_info_struct *sis,
+ struct file *swap_file)
{
while (!RB_EMPTY_ROOT(&sis->swap_extent_root)) {
struct rb_node *rb = sis->swap_extent_root.rb_node;
@@ -2532,7 +2534,6 @@ static void destroy_swap_extents(struct swap_info_struct *sis)
}
if (sis->flags & SWP_ACTIVATED) {
- struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;
sis->flags &= ~SWP_ACTIVATED;
@@ -2615,9 +2616,9 @@ EXPORT_SYMBOL_GPL(add_swap_extent);
* Typically it is in the 1-4 megabyte range. So we can have hundreds of
* extents in the rbtree. - akpm.
*/
-static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
+static int setup_swap_extents(struct swap_info_struct *sis,
+ struct file *swap_file, sector_t *span)
{
- struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;
struct inode *inode = mapping->host;
int ret;
@@ -2635,7 +2636,7 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
sis->flags |= SWP_ACTIVATED;
if ((sis->flags & SWP_FS_OPS) &&
sio_pool_init() != 0) {
- destroy_swap_extents(sis);
+ destroy_swap_extents(sis, swap_file);
return -ENOMEM;
}
return ret;
@@ -2851,7 +2852,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
flush_work(&p->reclaim_work);
flush_percpu_swap_cluster(p);
- destroy_swap_extents(p);
+ destroy_swap_extents(p, p->swap_file);
if (p->flags & SWP_CONTINUED)
free_swap_count_continuations(p);
@@ -2941,7 +2942,7 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
return SEQ_START_TOKEN;
for (type = 0; (si = swap_type_to_info(type)); type++) {
- if (!(si->flags & SWP_USED) || !si->swap_map)
+ if (!(si->swap_file))
continue;
if (!--l)
return si;
@@ -2962,7 +2963,7 @@ static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
++(*pos);
for (; (si = swap_type_to_info(type)); type++) {
- if (!(si->flags & SWP_USED) || !si->swap_map)
+ if (!(si->swap_file))
continue;
return si;
}
@@ -3379,7 +3380,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
}
- si->swap_file = swap_file;
mapping = swap_file->f_mapping;
dentry = swap_file->f_path.dentry;
inode = mapping->host;
@@ -3429,7 +3429,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
si->max = maxpages;
si->pages = maxpages - 1;
- nr_extents = setup_swap_extents(si, &span);
+ nr_extents = setup_swap_extents(si, swap_file, &span);
if (nr_extents < 0) {
error = nr_extents;
goto bad_swap_unlock_inode;
@@ -3538,6 +3538,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
prio = DEF_SWAP_PRIO;
if (swap_flags & SWAP_FLAG_PREFER)
prio = swap_flags & SWAP_FLAG_PRIO_MASK;
+
+ si->swap_file = swap_file;
enable_swap_info(si, prio, swap_map, cluster_info, zeromap);
pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s\n",
@@ -3562,10 +3564,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
kfree(si->global_cluster);
si->global_cluster = NULL;
inode = NULL;
- destroy_swap_extents(si);
+ destroy_swap_extents(si, swap_file);
swap_cgroup_swapoff(si->type);
spin_lock(&swap_lock);
- si->swap_file = NULL;
si->flags = 0;
spin_unlock(&swap_lock);
vfree(swap_map);
--
2.52.0
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