exfat: use kvmalloc_array/kvfree instead of kmalloc_array/kfree

The call stack shown below is a scenario in the Linux 4.19 kernel.
Allocating memory failed where exfat fs use kmalloc_array due to
system memory fragmentation, while the u-disk was inserted without
recognition.
Devices such as u-disk using the exfat file system are pluggable and
may be insert into the system at any time.
However, long-term running systems cannot guarantee the continuity of
physical memory. Therefore, it's necessary to address this issue.

Binder:2632_6: page allocation failure: order:4,
 mode:0x6040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null)
Call trace:
[242178.097582]  dump_backtrace+0x0/0x4
[242178.097589]  dump_stack+0xf4/0x134
[242178.097598]  warn_alloc+0xd8/0x144
[242178.097603]  __alloc_pages_nodemask+0x1364/0x1384
[242178.097608]  kmalloc_order+0x2c/0x510
[242178.097612]  kmalloc_order_trace+0x40/0x16c
[242178.097618]  __kmalloc+0x360/0x408
[242178.097624]  load_alloc_bitmap+0x160/0x284
[242178.097628]  exfat_fill_super+0xa3c/0xe7c
[242178.097635]  mount_bdev+0x2e8/0x3a0
[242178.097638]  exfat_fs_mount+0x40/0x50
[242178.097643]  mount_fs+0x138/0x2e8
[242178.097649]  vfs_kern_mount+0x90/0x270
[242178.097655]  do_mount+0x798/0x173c
[242178.097659]  ksys_mount+0x114/0x1ac
[242178.097665]  __arm64_sys_mount+0x24/0x34
[242178.097671]  el0_svc_common+0xb8/0x1b8
[242178.097676]  el0_svc_handler+0x74/0x90
[242178.097681]  el0_svc+0x8/0x340

By analyzing the exfat code,we found that continuous physical memory
is not required here,so kvmalloc_array is used can solve this problem.

Cc: [email protected]
Signed-off-by: gaoming <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

Author: gaoming

fs/exfat/balloc.c

@@ -69,7 +69,7 @@ static int exfat_allocate_bitmap(struct super_block *sb,
 	}
 	sbi->map_sectors = ((need_map_size - 1) >>
 			(sb->s_blocksize_bits)) + 1;
-	sbi->vol_amap = kmalloc_array(sbi->map_sectors,
+	sbi->vol_amap = kvmalloc_array(sbi->map_sectors,
 				sizeof(struct buffer_head *), GFP_KERNEL);
 	if (!sbi->vol_amap)
 		return -ENOMEM;
@@ -84,7 +84,7 @@ static int exfat_allocate_bitmap(struct super_block *sb,
 			while (j < i)
 				brelse(sbi->vol_amap[j++]);
 
-			kfree(sbi->vol_amap);
+			kvfree(sbi->vol_amap);
 			sbi->vol_amap = NULL;
 			return -EIO;
 		}
@@ -138,7 +138,7 @@ void exfat_free_bitmap(struct exfat_sb_info *sbi)
 	for (i = 0; i < sbi->map_sectors; i++)
 		__brelse(sbi->vol_amap[i]);
 
-	kfree(sbi->vol_amap);
+	kvfree(sbi->vol_amap);
 }
 
 int exfat_set_bitmap(struct inode *inode, unsigned int clu, bool sync)