ext4: use private version of page_zero_new_buffers() for data=journal mode (b90197b6) · Commits · 戴 / test

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 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:

Theodore Ts'o <tytso@mit.edu> Reviewed-by:

Jan Kara <jack@suse.com>

fs/ext4/inode.c

+33 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1181,6 +1181,38 @@ errout:
	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,

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