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 <namjae.jeon@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 16 insertions, 0 deletions

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index e0c4ba39a377..64e295e8ff38 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -370,6 +370,7 @@ 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);
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 85f79a89e747..8429c68e3057 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -443,6 +443,9 @@ 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);
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 756aead10d96..7b41a2dcdd76 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -294,6 +294,18 @@ 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,