The current non rotational check is unreliable
as the device's rotational status can be changed by a user via sysfs.

Use the more reliable SWP_SOLIDSTATE flag which is set at swapon time,
to ensure the nr_rotate_swap count remains consistent.
Plus, it is easy to read and simple.

Fixes: 81a0298bdfab ("mm, swap: don't use VMA based swap readahead if HDD is used as swap")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ed2c8e4edb71..b7cde8ef6742 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2913,7 +2913,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	if (p->flags & SWP_CONTINUED)
 		free_swap_count_continuations(p);
 
-	if (!p->bdev || !bdev_nonrot(p->bdev))
+	if (!(p->flags & SWP_SOLIDSTATE))
 		atomic_dec(&nr_rotate_swap);
 
 	mutex_lock(&swapon_mutex);
-- 
2.34.1