sys_swapon: separate final enabling of the swapfile

The block in sys_swapon which does the final adjustments to the
swap_info_struct and to swap_list is the same as the block which
re-inserts it again at sys_swapoff on failure of try_to_unuse(). Move
this code to a separate function, and use it both in sys_swapon and
sys_swapoff.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Tested-by: Eric B Munson <emunson@mgebm.net>
Acked-by: Eric B Munson <emunson@mgebm.net>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 42 insertions, 42 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 465d972f4c7c..7243044c4139 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1550,6 +1550,36 @@ bad_bmap:
         goto out;
 }
 
+static void enable_swap_info(struct swap_info_struct *p, int prio,
+                                unsigned char *swap_map)
+{
+        int i, prev;
+
+        spin_lock(&swap_lock);
+        if (prio >= 0)
+                p->prio = prio;
+        else
+                p->prio = --least_priority;
+        p->swap_map = swap_map;
+        p->flags |= SWP_WRITEOK;
+        nr_swap_pages += p->pages;
+        total_swap_pages += p->pages;
+
+        /* insert swap space into swap_list: */
+        prev = -1;
+        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
+                if (p->prio >= swap_info[i]->prio)
+                        break;
+                prev = i;
+        }
+        p->next = i;
+        if (prev < 0)
+                swap_list.head = swap_list.next = p->type;
+        else
+                swap_info[prev]->next = p->type;
+        spin_unlock(&swap_lock);
+}
+
 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
         struct swap_info_struct *p = NULL;
@@ -1621,26 +1651,14 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
         current->flags &= ~PF_OOM_ORIGIN;
 
         if (err) {
+                /*
+                 * reading p->prio and p->swap_map outside the lock is
+                 * safe here because only sys_swapon and sys_swapoff
+                 * change them, and there can be no other sys_swapon or
+                 * sys_swapoff for this swap_info_struct at this point.
+                 */
                 /* re-insert swap space back into swap_list */
-                spin_lock(&swap_lock);
-                if (p->prio < 0)
-                        p->prio = --least_priority;
-                p->flags |= SWP_WRITEOK;
-                nr_swap_pages += p->pages;
-                total_swap_pages += p->pages;
-
-                prev = -1;
-                for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
-                        if (p->prio >= swap_info[i]->prio)
-                                break;
-                        prev = i;
-                }
-                p->next = i;
-                if (prev < 0)
-                        swap_list.head = swap_list.next = type;
-                else
-                        swap_info[prev]->next = type;
-                spin_unlock(&swap_lock);
+                enable_swap_info(p, p->prio, p->swap_map);
                 goto out_dput;
         }
 
@@ -2037,7 +2055,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         char *name;
         struct file *swap_file = NULL;
         struct address_space *mapping;
-        int i, prev;
+        int i;
+        int prio;
         int error;
         union swap_header *swap_header;
         int nr_extents;
@@ -2134,30 +2153,11 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         }
 
         mutex_lock(&swapon_mutex);
-        spin_lock(&swap_lock);
+        prio = -1;
         if (swap_flags & SWAP_FLAG_PREFER)
-                p->prio =
+                prio =
                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
-        else
-                p->prio = --least_priority;
-        p->swap_map = swap_map;
-        p->flags |= SWP_WRITEOK;
-        nr_swap_pages += p->pages;
-        total_swap_pages += p->pages;
-
-        /* insert swap space into swap_list: */
-        prev = -1;
-        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
-                if (p->prio >= swap_info[i]->prio)
-                        break;
-                prev = i;
-        }
-        p->next = i;
-        if (prev < 0)
-                swap_list.head = swap_list.next = p->type;
-        else
-                swap_info[prev]->next = p->type;
-        spin_unlock(&swap_lock);
+        enable_swap_info(p, prio, swap_map);
 
         printk(KERN_INFO "Adding %uk swap on %s.  "
                         "Priority:%d extents:%d across:%lluk %s%s\n",