[PATCH] ext4: fix divide error in ext4_mb_regular_allocator

[Edward Adam Davis <eadavis@qq.com>]

Before determining that the goal length is a multiple of the stripe size,
check CR_GOAL_LEN_FAST and CR_BEST_AVAIL_LEN first.

Fixes: 1f6bc02f1848 ("ext4: fallback to complex scan if aligned scan doesn't work")
Reported-and-tested-by: syzbot+1ad8bac5af24d01e2cbd@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1ad8bac5af24d01e2cbd
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/ext4/mballoc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 9dda9cd68ab2..451f92cde461 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2928,13 +2928,12 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 			if (cr == CR_POWER2_ALIGNED)
 				ext4_mb_simple_scan_group(ac, &e4b);
 			else {
-				bool is_stripe_aligned = sbi->s_stripe &&
+				bool is_stripe_aligned = (cr == CR_GOAL_LEN_FAST ||
+					cr == CR_BEST_AVAIL_LEN) && sbi->s_stripe &&
 					!(ac->ac_g_ex.fe_len %
 					  EXT4_B2C(sbi, sbi->s_stripe));
 
-				if ((cr == CR_GOAL_LEN_FAST ||
-				     cr == CR_BEST_AVAIL_LEN) &&
-				    is_stripe_aligned)
+				if (is_stripe_aligned)
 					ext4_mb_scan_aligned(ac, &e4b);
 
 				if (ac->ac_status == AC_STATUS_CONTINUE)
-- 
2.43.0