md/raid5: make sure stripe_size as power of two

Commit 3b5408b9 ("md/raid5: support config stripe_size by sysfs
entry") make stripe_size as a configurable value. It just requires
stripe_size as multiple of 4KB.

In fact, we should make sure stripe_size as power of two. Otherwise,
stripe_shift which is the result of ilog2 can not represent the real
stripe_size. Then, stripe_hash() and stripe_hash_locks_hash() may
get unexpected value.

Fixes: 3b5408b9 ("md/raid5: support config stripe_size by sysfs entry")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/raid5.c

@@ -6514,9 +6514,12 @@ raid5_store_stripe_size(struct mddev  *mddev, const char *page, size_t len)
 
 	/*
 	 * The value should not be bigger than PAGE_SIZE. It requires to
-	 * be multiple of DEFAULT_STRIPE_SIZE.
+	 * be multiple of DEFAULT_STRIPE_SIZE and the value should be power
+	 * of two.
 	 */
-	if (new % DEFAULT_STRIPE_SIZE != 0 || new > PAGE_SIZE || new == 0)
+	if (new % DEFAULT_STRIPE_SIZE != 0 ||
+			new > PAGE_SIZE || new == 0 ||
+			new != roundup_pow_of_two(new))
 		return -EINVAL;
 
 	err = mddev_lock(mddev);