ext4: Widen type of ext4_sb_info.s_mb_maxs[]

I chased the cause of following ext4 oops report which is tested on
ia64 box.

http://bugzilla.kernel.org/show_bug.cgi?id=12018

The cause is the size of s_mb_maxs array that is defined as "unsigned
short" in ext4_sb_info structure.  If the file system's block size is
8k or greater, an unsigned short is not wide enough to contain the
value fs->blocksize << 3.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: stable@kernel.org

fs/ext4/ext4_sb.h

@@ -102,7 +102,8 @@ struct ext4_sb_info {
 	spinlock_t s_reserve_lock;
 	spinlock_t s_md_lock;
 	tid_t s_last_transaction;
-	unsigned short *s_mb_offsets, *s_mb_maxs;
+	unsigned short *s_mb_offsets;
+	unsigned int *s_mb_maxs;
 
 	/* tunables */
 	unsigned long s_stripe;

fs/ext4/mballoc.c

@@ -2493,6 +2493,8 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
 	if (sbi->s_mb_offsets == NULL) {
 		return -ENOMEM;
 	}
+
+	i = (sb->s_blocksize_bits + 2) * sizeof(unsigned int);
 	sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
 	if (sbi->s_mb_maxs == NULL) {
 		kfree(sbi->s_mb_maxs);