!14271 iomap: fix zero padding data issue in concurrent append writes

{

	struct iomap_folio_state *ifs = folio->private;

	size_t poff = offset_in_folio(folio, pos);

	loff_t isize = i_size_read(inode);

	int error;

	if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos)) {

	if (ifs)

		atomic_add(len, &ifs->write_bytes_pending);

	/*

	 * Clamp io_offset and io_size to the incore EOF so that ondisk

	 * file size updates in the ioend completion are byte-accurate.

	 * This avoids recovering files with zeroed tail regions when

	 * writeback races with appending writes:

	 *

	 *    Thread 1:                  Thread 2:

	 *    ------------               -----------

	 *    write [A, A+B]

	 *    update inode size to A+B

	 *    submit I/O [A, A+BS]

	 *                               write [A+B, A+B+C]

	 *                               update inode size to A+B+C

	 *    <I/O completes, updates disk size to min(A+B+C, A+BS)>

	 *    <power failure>

	 *

	 *  After reboot:

	 *    1) with A+B+C < A+BS, the file has zero padding in range

	 *       [A+B, A+B+C]

	 *

	 *    |<     Block Size (BS)   >|

	 *    |DDDDDDDDDDDD0000000000000|

	 *    ^           ^        ^

	 *    A          A+B     A+B+C

	 *                       (EOF)

	 *

	 *    2) with A+B+C > A+BS, the file has zero padding in range

	 *       [A+B, A+BS]

	 *

	 *    |<     Block Size (BS)   >|<     Block Size (BS)    >|

	 *    |DDDDDDDDDDDD0000000000000|00000000000000000000000000|

	 *    ^           ^             ^           ^

	 *    A          A+B           A+BS       A+B+C

	 *                             (EOF)

	 *

	 *    D = Valid Data

	 *    0 = Zero Padding

	 *

	 * Note that this defeats the ability to chain the ioends of

	 * appending writes. Writeback beyond EOF block may occur in

	 * concurrent scenarios(e.g. racing with truncate) and io_size

	 * should not be trimmed in such cases.

	 */

	wpc->ioend->io_size += len;

	if (pos < isize && pos + len > isize)

		wpc->ioend->io_size = isize - wpc->ioend->io_offset;

	wbc_account_cgroup_owner(wbc, &folio->page, len);

	return 0;

}

	u16			io_type;

	u16			io_flags;	/* IOMAP_F_* */

	struct inode		*io_inode;	/* file being written to */

	size_t			io_size;	/* size of the extent */

	size_t			io_size;	/* size of data within eof */

	loff_t			io_offset;	/* offset in the file */

	sector_t		io_sector;	/* start sector of ioend */

	struct bio		io_bio;		/* MUST BE LAST! */