[PATCH] ext4: avoid oversized shift in ext4_fill_flex_info()

Commit 503358ae fixed a division by zero, but groups_per_flex still
overflows due to an oversized shift, given a large s_log_groups_per_flex
like 36.  (1 << 36) is undefined in C; the result may vary depending
on the architecture, e.g., 16 on x86, thus bypassing the sanity check
(groups_per_flex < 2).

Signed-off-by: Xi Wang <xi.wang@gmail.com>
---
 fs/ext4/super.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3e1329e..6deaf41 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2010,14 +2010,15 @@ static int ext4_fill_flex_info(struct super_block *sb)
 	size_t size;
 	int i;
 
-	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
-	groups_per_flex = 1 << sbi->s_log_groups_per_flex;