mm: fix nr_rotate_swap leak in swapon() error case

If swapon() fails after incrementing nr_rotate_swap, we don't decrement
it and thus effectively leak it.  Make sure we decrement it if we
incremented it.

Link: http://lkml.kernel.org/r/b6fe6b879f17fa68eee6cbd876f459f6e5e33495.1526491581.git.osandov@fb.com
Fixes: 81a0298bdfab ("mm, swap: don't use VMA based swap readahead if HDD is used as swap")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index cc2cf04d9018..78a015fcec3b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3112,6 +3112,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
         unsigned long *frontswap_map = NULL;
         struct page *page = NULL;
         struct inode *inode = NULL;
+        bool inced_nr_rotate_swap = false;
 
         if (swap_flags & ~SWAP_FLAGS_VALID)
                 return -EINVAL;
@@ -3215,8 +3216,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
                         cluster = per_cpu_ptr(p->percpu_cluster, cpu);
                         cluster_set_null(&cluster->index);
                 }
-        } else
+        } else {
                 atomic_inc(&nr_rotate_swap);
+                inced_nr_rotate_swap = true;
+        }
 
         error = swap_cgroup_swapon(p->type, maxpages);
         if (error)
@@ -3307,6 +3310,8 @@ bad_swap:
         vfree(swap_map);
         kvfree(cluster_info);
         kvfree(frontswap_map);
+        if (inced_nr_rotate_swap)
+                atomic_dec(&nr_rotate_swap);
         if (swap_file) {
                 if (inode && S_ISREG(inode->i_mode)) {
                         inode_unlock(inode);