From: Kairui Song <kasong@tencent.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@tencent.com>
---
mm/swapfile.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 32e0e7545ab8..25dfe992538d 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);
@@ -2532,7 +2533,8 @@ 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;
@@ -2543,7 +2545,6 @@ 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;
@@ -2626,9 +2627,9 @@ 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;
@@ -2646,7 +2647,7 @@ 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;
@@ -2862,7 +2863,7 @@ 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);
@@ -2952,7 +2953,7 @@ 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;
@@ -2973,7 +2974,7 @@ 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;
}
@@ -3390,7 +3391,6 @@ 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;
@@ -3440,7 +3440,7 @@ 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;
@@ -3549,6 +3549,8 @@ 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",
@@ -3573,10 +3575,9 @@ 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);
--
2.52.0Acked-by: Chris Li <chrisl@kernel.org>
Chris
On Tue, Feb 17, 2026 at 12:06 PM Kairui Song via B4 Relay
<devnull+kasong.tencent.com@kernel.org> wrote:
>
> From: Kairui Song <kasong@tencent.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@tencent.com>
> ---
> mm/swapfile.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 32e0e7545ab8..25dfe992538d 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);
> @@ -2532,7 +2533,8 @@ 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;
> @@ -2543,7 +2545,6 @@ 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;
> @@ -2626,9 +2627,9 @@ 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;
> @@ -2646,7 +2647,7 @@ 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;
> @@ -2862,7 +2863,7 @@ 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);
>
> @@ -2952,7 +2953,7 @@ 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;
> @@ -2973,7 +2974,7 @@ 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;
> }
> @@ -3390,7 +3391,6 @@ 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;
> @@ -3440,7 +3440,7 @@ 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;
> @@ -3549,6 +3549,8 @@ 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",
> @@ -3573,10 +3575,9 @@ 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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