[PATCH] vfat: fix uninitialized i_pos error

[zhoumin]

The i_pos field remains uninitialized when fat_fs_error_ratelimit() reports
error, e.g.,

	[ 1642.703550] FAT-fs (loop0): error, fat_get_cluster: invalid
	cluster chain (i_pos 0)

Since i_pos is assigned in fat_attach after fat_fill_inode, the error
message lacks useful debug info.

Path:
vfat_lookup
	fat_build_inode
		fat_fill_inode
			fat_calc_dir_size
          			fat_get_cluster /* report error */
      	fat_attach  /* i_pos assigned here */

Reproduction steps:
dd if=/dev/zero of=/tmp/fatfile bs=1M count=1024 && \
mkfs.vfat -I /tmp/fatfile && \
fsck.vfat -bv /tmp/fatfile && \
mount -t vfat /tmp/fatfile /mnt/vfat && \
mkdir /mnt/vfat/dir1 && \
for i in `seq 1 500`;do touch /mnt/vfat/dir1/fatregfiletest.${i};done && \
dd if=/dev/zero of=/dev/loop0 bs=1 count=1 seek=$((16384+0x1C)) && \
sync && echo 3 > /proc/sys/vm/drop_caches && \
ls /mnt/vfat/dir1/

Signed-off-by: zhoumin <teczm@xxxxxxxxxxx>
---
 fs/fat/inode.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 3852bb66358c..c71f08b20617 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -405,7 +405,6 @@ void fat_attach(struct inode *inode, loff_t i_pos)
 					  + fat_hash(i_pos);
 
 		spin_lock(&sbi->inode_hash_lock);
-		MSDOS_I(inode)->i_pos = i_pos;
 		hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head);
 		spin_unlock(&sbi->inode_hash_lock);
 	}
@@ -429,7 +428,6 @@ void fat_detach(struct inode *inode)
 {
 	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
 	spin_lock(&sbi->inode_hash_lock);
-	MSDOS_I(inode)->i_pos = 0;
 	hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
 	spin_unlock(&sbi->inode_hash_lock);
 
@@ -513,7 +511,6 @@ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
 	struct timespec64 mtime;
 	int error;
 
-	MSDOS_I(inode)->i_pos = 0;
 	inode->i_uid = sbi->options.fs_uid;
 	inode->i_gid = sbi->options.fs_gid;
 	inode_inc_iversion(inode);
@@ -604,6 +601,7 @@ struct inode *fat_build_inode(struct super_block *sb,
 		goto out;
 	}
 	inode->i_ino = iunique(sb, MSDOS_ROOT_INO);
+	MSDOS_I(inode)->i_pos = i_pos;
 	inode_set_iversion(inode, 1);
 	err = fat_fill_inode(inode, de);
 	if (err) {
-- 
2.43.0