fat: fix data past EOF resulting from fsx testsuite

When running FSX with direct I/O mode, fsx resulted in DATA past EOF issues.

fsx ./file2 -Z -r 4096 -w 4096
...
..
truncating to largest ever: 0x907c
fallocating to largest ever: 0x11137
truncating to largest ever: 0x2c6fe
truncating to largest ever: 0x2cfdf
fallocating to largest ever: 0x40000
Mapped Read: non-zero data past EOF (0x18628) page offset 0x629 is 0x2a4e
...
..

The reason being, it is doing a truncate down, but the zeroing does not happen on the last block boundary when offset is not aligned. Even though it calls truncate_setsize()->truncate_inode_pages()-> truncate_inode_pages_range() and considers the partial zeroout but it retrieves the page using find_lock_page() - which only looks the page in the cache. So, zeroing out does not happen in case of direct IO.

Make a truncate page based around block_truncate_page for FAT filesystem and invoke that helper to zerout in case the offset is not aligned with the blocksize.

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

Signed-off-by Amit Sahrawat <[email protected]>

---
 fs/fat/fat.h   |  1 +
 fs/fat/file.c  |  3 +++
 fs/fat/inode.c | 12 ++++++++++++
 3 files changed, 16 insertions(+)

fs/fat/fat.h +1 -0

index eff027d..61801da 100644
@@ -374,6 +374,7 @@ extern int fat_file_fsync(struct file *file, loff_t start, loff_t end,
 			  int datasync);
 
 /* fat/inode.c */
+extern int fat_block_truncate_page(struct inode *inode, loff_t from);
 extern void fat_attach(struct inode *inode, loff_t i_pos);
 extern void fat_detach(struct inode *inode);
 extern struct inode *fat_iget(struct super_block *sb, loff_t i_pos);

fs/fat/file.c +3 -0

index f2c73ae..757fc20 100644
@@ -523,6 +523,9 @@ int fat_setattr(struct dentry *dentry, struct iattr *attr)
 	}
 
 	if (attr->ia_valid & ATTR_SIZE) {
+		error = fat_block_truncate_page(inode, attr->ia_size);
+		if (error)
+			goto out;
 		down_write(&MSDOS_I(inode)->truncate_lock);
 		truncate_setsize(inode, attr->ia_size);
 		fat_truncate_blocks(inode, attr->ia_size);

fs/fat/inode.c +12 -0

index f362796..9bf44eb 100644
@@ -339,6 +339,18 @@ static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
 	return blocknr;
 }
 
+/*
+ * fat_block_truncate_page() zeroes out a mapping from file offset `from'
+ * up to the end of the block which corresponds to `from'.
+ * This is required during truncate to physically zeroout the tail end
+ * of that block so it doesn't yield old data if the file is later grown.
+ * Also, avoid causing failure from fsx for cases of "data past EOF"
+ */
+int fat_block_truncate_page(struct inode *inode, loff_t from)
+{
+	return block_truncate_page(inode->i_mapping, from, fat_get_block);
+}
+
 static const struct address_space_operations fat_aops = {
 	.readpage	= fat_readpage,
 	.readpages	= fat_readpages,