Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b90197b6 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

ext4: use private version of page_zero_new_buffers() for data=journal mode 



If there is a error while copying data from userspace into the page
cache during a write(2) system call, in data=journal mode, in
ext4_journalled_write_end() were using page_zero_new_buffers() from
fs/buffer.c.  Unfortunately, this sets the buffer dirty flag, which is
no good if journalling is enabled.  This is a long-standing bug that
goes back for years and years in ext3, but a combination of (a)
data=journal not being very common, (b) in many case it only results
in a warning message. and (c) only very rarely causes the kernel hang,
means that we only really noticed this as a problem when commit
998ef75d caused this failure to happen frequently enough to cause
generic/208 to fail when run in data=journal mode.

The fix is to have our own version of this function that doesn't call
mark_dirty_buffer(), since we will end up calling
ext4_handle_dirty_metadata() on the buffer head(s) in questions very
shortly afterwards in ext4_journalled_write_end().

Thanks to Dave Hansen and Linus Torvalds for helping to identify the
root cause of the problem.

Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJan Kara <jack@suse.com>
parent 36086d43

fs/ext4/inode.c

+33 −1
Original line number Original line Diff line number Diff line
@@ -1181,6 +1181,38 @@ static int ext4_write_end(struct file *file, 
	return ret ? ret : copied;

	return ret ? ret : copied;

}

}





/*

 * This is a private version of page_zero_new_buffers() which doesn't

 * set the buffer to be dirty, since in data=journalled mode we need

 * to call ext4_handle_dirty_metadata() instead.

 */

static void zero_new_buffers(struct page *page, unsigned from, unsigned to)

{

	unsigned int block_start = 0, block_end;

	struct buffer_head *head, *bh;



	bh = head = page_buffers(page);

	do {

		block_end = block_start + bh->b_size;

		if (buffer_new(bh)) {

			if (block_end > from && block_start < to) {

				if (!PageUptodate(page)) {

					unsigned start, size;



					start = max(from, block_start);

					size = min(to, block_end) - start;



					zero_user(page, start, size);

					set_buffer_uptodate(bh);

				}

				clear_buffer_new(bh);

			}

		}

		block_start = block_end;

		bh = bh->b_this_page;

	} while (bh != head);

}



static int ext4_journalled_write_end(struct file *file,

static int ext4_journalled_write_end(struct file *file,

				     struct address_space *mapping,

				     struct address_space *mapping,

				     loff_t pos, unsigned len, unsigned copied,

				     loff_t pos, unsigned len, unsigned copied,
@@ -1207,7 +1239,7 @@ static int ext4_journalled_write_end(struct file *file, 
		if (copied < len) {

		if (copied < len) {

			if (!PageUptodate(page))

			if (!PageUptodate(page))

				copied = 0;

				copied = 0;

			page_zero_new_buffers(page, from+copied, to);

			zero_new_buffers(page, from+copied, to);

		}

		}





		ret = ext4_walk_page_buffers(handle, page_buffers(page), from,

		ret = ext4_walk_page_buffers(handle, page_buffers(page), from,