[RFC,1/2] ext4: add a version of convert_inline_data_nolock() for regular files
diff mbox

Message ID 20170606000359.16794-1-tytso@mit.edu
State New
Headers show

Commit Message

Theodore Ts'o June 6, 2017, 12:03 a.m. UTC
The current version of ext4_convert_inline_data_nolock() should not be
used for regular files, since it does the conversion via using jbd2,
and this if we are not using data journalling, this is unsafe.  If the
data block is updated after the inode is converted from using inline
data to using a data block, when the journal is replayed, the new
version of the data block can get overwritten by the old version of
the data block.

The ext4_convert_inline_data_nolock() also doesn't handle races with
Direct I/O correctly.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/inline.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 107 insertions(+), 3 deletions(-)

Comments

Eric Biggers June 7, 2017, 3:47 a.m. UTC | #1
Hi Ted,

On Mon, Jun 05, 2017 at 08:03:58PM -0400, Theodore Ts'o wrote:
> The current version of ext4_convert_inline_data_nolock() should not be
> used for regular files, since it does the conversion via using jbd2,
> and this if we are not using data journalling, this is unsafe.  If the
> data block is updated after the inode is converted from using inline
> data to using a data block, when the journal is replayed, the new
> version of the data block can get overwritten by the old version of
> the data block.

Thanks for trying to fix this mess!  I'm not sure I know enough to fully review
it, but here are some things I'm questioning...

> 
> The ext4_convert_inline_data_nolock() also doesn't handle races with
> Direct I/O correctly.
> 

Are you sure direct I/O is an issue?   ext4_direct_IO() doesn't support files
with inline data; it returns 0 if 'ext4_has_inline_data(inode)'.

>  /*
> + * Only used for regular files, not directories!
> + *
> + * The inode and page must be locked when this function is called.
> + */
> +static int reg_convert_inline_data_nolock(handle_t *handle,
> +					  struct inode *inode,
> +					  struct page *page,
> +					  struct ext4_iloc *iloc)
> +{
> +	int error;
> +	struct buffer_head *data_bh = NULL;
> +	int inline_size = ext4_get_inline_size(inode);
> +
> +	if (!(inode->i_state & (I_NEW|I_FREEING)))
> +		WARN_ON(!inode_is_locked(inode));

I don't think the inode lock is guaranteed... ext4_convert_inline_data() is
called from ext4_fallocate() and ext4_page_mkwrite() without out.  It seems the
xattr_sem will always be taken for write, though.

> +
> +	/* If some one has already done this for us, just exit. */
> +	if (!ext4_has_inline_data(inode))
> +		return 0;
> +
> +	if (!PageUptodate(page)) {
> +		error = ext4_read_inline_page(inode, page);
> +		if (error < 0)
> +			return error;
> +	}
> +
> +	/* Avoid races with DIO */
> +	ext4_inode_block_unlocked_dio(inode);

What is ext4_inode_block_unlocked_dio() even supposed to do?  It sets
EXT4_STATE_DIOREAD_LOCK but nothing seems to check it.


> +	inode_dio_wait(inode);
> +
> +	error = ext4_destroy_inline_data_nolock(handle, inode);
> +	if (error)
> +		return error;
> +
> +	error = __block_write_begin(page, 0, inline_size, ext4_get_block);
> +	if (error)
> +		goto out_restore;
> +
> +	data_bh = page_buffers(page);
> +	BUG_ON(data_bh == NULL);
> +
> +	if (ext4_should_journal_data(inode)) {
> +		lock_buffer(data_bh);
> +		error = ext4_journal_get_create_access(handle, data_bh);
> +		if (error) {
> +			unlock_buffer(data_bh);
> +			error = -EIO;
> +			goto out_restore;
> +		}
> +		error = ext4_handle_dirty_metadata(handle, inode, data_bh);
> +		unlock_buffer(data_bh);
> +	} else {
> +		__set_page_dirty_buffers(page);
> +		if (ext4_should_order_data(inode))
> +			error = ext4_jbd2_inode_add_write(handle, inode);
> +	}
> +
> +out_restore:
> +	if (error) {
> +		void *kaddr = kmap_atomic(page);

kmap(), not kmap_atomic(), since the stuff in between can block.

>  
> +	if (S_ISREG(inode->i_mode)) {
> +		page = grab_cache_page_write_begin(inode->i_mapping, 0, 0);
> +		if (!page)
> +			return -ENOMEM;
> +	}
> +
>  	handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
>  	if (IS_ERR(handle)) {
>  		error = PTR_ERR(handle);
> @@ -2027,11 +2121,21 @@ int ext4_convert_inline_data(struct inode *inode)
>  	}

Doesn't the page lock rank below transaction start?

Eric

Patch
diff mbox

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 8d141c0c8ff9..c9e3a262f27f 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1259,6 +1259,79 @@  static int ext4_convert_inline_data_nolock(handle_t *handle,
 }
 
 /*
+ * Only used for regular files, not directories!
+ *
+ * The inode and page must be locked when this function is called.
+ */
+static int reg_convert_inline_data_nolock(handle_t *handle,
+					  struct inode *inode,
+					  struct page *page,
+					  struct ext4_iloc *iloc)
+{
+	int error;
+	struct buffer_head *data_bh = NULL;
+	int inline_size = ext4_get_inline_size(inode);
+
+	if (!(inode->i_state & (I_NEW|I_FREEING)))
+		WARN_ON(!inode_is_locked(inode));
+
+	/* If some one has already done this for us, just exit. */
+	if (!ext4_has_inline_data(inode))
+		return 0;
+
+	if (!PageUptodate(page)) {
+		error = ext4_read_inline_page(inode, page);
+		if (error < 0)
+			return error;
+	}
+
+	/* Avoid races with DIO */
+	ext4_inode_block_unlocked_dio(inode);
+	inode_dio_wait(inode);
+
+	error = ext4_destroy_inline_data_nolock(handle, inode);
+	if (error)
+		return error;
+
+	error = __block_write_begin(page, 0, inline_size, ext4_get_block);
+	if (error)
+		goto out_restore;
+
+	data_bh = page_buffers(page);
+	BUG_ON(data_bh == NULL);
+
+	if (ext4_should_journal_data(inode)) {
+		lock_buffer(data_bh);
+		error = ext4_journal_get_create_access(handle, data_bh);
+		if (error) {
+			unlock_buffer(data_bh);
+			error = -EIO;
+			goto out_restore;
+		}
+		error = ext4_handle_dirty_metadata(handle, inode, data_bh);
+		unlock_buffer(data_bh);
+	} else {
+		__set_page_dirty_buffers(page);
+		if (ext4_should_order_data(inode))
+			error = ext4_jbd2_inode_add_write(handle, inode);
+	}
+
+out_restore:
+	if (error) {
+		void *kaddr = kmap_atomic(page);
+
+		if (data_bh)
+			ext4_free_blocks(handle, inode, data_bh, 0, 1, 0);
+		ext4_create_inline_data(handle, inode, inline_size);
+		ext4_write_inline_data(inode, iloc, kaddr, 0, inline_size);
+		ext4_set_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
+		kunmap_atomic(kaddr);
+	}
+	ext4_inode_resume_unlocked_dio(inode);
+	return error;
+}
+
+/*
  * Try to add the new entry to the inline data.
  * If succeeds, return 0. If not, extended the inline dir and copied data to
  * the new created block.
@@ -1898,7 +1971,21 @@  int ext4_try_to_evict_inline_data(handle_t *handle,
 		goto out;
 	}
 
-	error = ext4_convert_inline_data_nolock(handle, inode, &iloc);
+	if (S_ISREG(inode->i_mode)) {
+		struct page *page;
+
+		page = grab_cache_page_write_begin(inode->i_mapping, 0,
+						   AOP_FLAG_NOFS);
+		if (!page) {
+			error = -ENOMEM;
+			goto out;
+		}
+		error = reg_convert_inline_data_nolock(handle, inode,
+						       page, &iloc);
+		unlock_page(page);
+		put_page(page);
+	} else
+		error = ext4_convert_inline_data_nolock(handle, inode, &iloc);
 out:
 	brelse(iloc.bh);
 	return error;
@@ -2007,6 +2094,7 @@  int ext4_convert_inline_data(struct inode *inode)
 	int error, needed_blocks, no_expand;
 	handle_t *handle;
 	struct ext4_iloc iloc;
+	struct page *page = NULL;
 
 	if (!ext4_has_inline_data(inode)) {
 		ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
@@ -2020,6 +2108,12 @@  int ext4_convert_inline_data(struct inode *inode)
 	if (error)
 		return error;
 
+	if (S_ISREG(inode->i_mode)) {
+		page = grab_cache_page_write_begin(inode->i_mapping, 0, 0);
+		if (!page)
+			return -ENOMEM;
+	}
+
 	handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
 	if (IS_ERR(handle)) {
 		error = PTR_ERR(handle);
@@ -2027,11 +2121,21 @@  int ext4_convert_inline_data(struct inode *inode)
 	}
 
 	ext4_write_lock_xattr(inode, &no_expand);
-	if (ext4_has_inline_data(inode))
-		error = ext4_convert_inline_data_nolock(handle, inode, &iloc);
+	if (ext4_has_inline_data(inode)) {
+		if (page)
+			error = reg_convert_inline_data_nolock(handle,
+							inode, page, &iloc);
+		else
+			error = ext4_convert_inline_data_nolock(handle, inode,
+								&iloc);
+	}
 	ext4_write_unlock_xattr(inode, &no_expand);
 	ext4_journal_stop(handle);
 out_free:
+	if (page) {
+		unlock_page(page);
+		put_page(page);
+	}
 	brelse(iloc.bh);
 	return error;
 }