sys_swapon: do not depend on "type" after allocation

Within sys_swapon, after the swap_info entry has been allocated, we
always have type == p->type and swap_info[type] == p. Use this fact to
reduce the dependency on the "type" local variable within the function,
as a preparation to move the allocation of the swap_info entry to a
separate function.

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.fujisu.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>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 9714644..5238d8d 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1927,7 +1927,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
        for (i = 0; i < nr_swapfiles; i++) {
                struct swap_info_struct *q = swap_info[i];
 
-               if (i == type || !q->swap_file)
+               if (q == p || !q->swap_file)
                        continue;
                if (mapping == q->swap_file->f_mapping)
                        goto bad_swap;
@@ -2062,7 +2062,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                }
        }
 
-       error = swap_cgroup_swapon(type, maxpages);
+       error = swap_cgroup_swapon(p->type, maxpages);
        if (error)
                goto bad_swap;
 
@@ -2120,9 +2120,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
        }
        p->next = i;
        if (prev < 0)
-               swap_list.head = swap_list.next = type;
+               swap_list.head = swap_list.next = p->type;
        else
-               swap_info[prev]->next = type;
+               swap_info[prev]->next = p->type;
        spin_unlock(&swap_lock);
        mutex_unlock(&swapon_mutex);
        atomic_inc(&proc_poll_event);
@@ -2136,7 +2136,7 @@ bad_swap:
                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
        }
        destroy_swap_extents(p);
-       swap_cgroup_swapoff(type);
+       swap_cgroup_swapoff(p->type);
 bad_swap_2:
        spin_lock(&swap_lock);
        p->swap_file = NULL;