On Thu, Sep 21, 2017 at 06:38:28PM +0800, Eryu Guan wrote:
> Since commit d531d91d6990 ("xfs: always use unwritten extents for
> direct I/O writes"), we start allocating unwritten extents for all
> direct writes to allow appending aio in XFS.
>
> But for dio writes that could extend file size we update the in-core
> inode size first, then convert the unwritten extents to real
> allocations at dio completion time in xfs_dio_write_end_io(). Thus a
> racing direct read could see the new i_size and find the unwritten
> extents first and read zeros instead of actual data, if the direct
> writer also takes a shared iolock.
>
> Fix it by updating the in-core inode size after the unwritten extent
> conversion. To do this, introduce a new boolean argument to
> xfs_iomap_write_unwritten() to tell if we want to update in-core
> i_size or not.
>
> Suggested-by: Brian Foster <bfoster@xxxxxxxxxx>
> Signed-off-by: Eryu Guan <eguan@xxxxxxxxxx>
> ---
>
> Patch passed the test posted by Eric[1] and a locally modified aio
> version of the test.
>
> I also ran fstests with config xfs_4k_crc, xfs_2k_reflink, xfs_1k_rmap
> and xfs_512, and aio-dio tests from ltp, I don't see any new failures
> introduced.
>
> [1] http://www.spinics.net/lists/fstests/msg06978.html
>
> fs/xfs/xfs_aops.c | 9 ++++++++-
> fs/xfs/xfs_file.c | 34 ++++++++++++++++++++--------------
> fs/xfs/xfs_iomap.c | 7 ++++++-
> fs/xfs/xfs_iomap.h | 2 +-
> fs/xfs/xfs_pnfs.c | 2 +-
> 5 files changed, 36 insertions(+), 18 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 29172609f2a3..f937968e9515 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -343,7 +343,14 @@ xfs_end_io(
> error = xfs_reflink_end_cow(ip, offset, size);
> break;
> case XFS_IO_UNWRITTEN:
> - error = xfs_iomap_write_unwritten(ip, offset, size);
> + /*
> + * The correct in-core inode size should have been updated by
> + * generic_write_end, and the 'size' here is buffer head
> + * granularity size of the ioend, which could be larger than
> + * the actual bytes written. So skip in-core i_size update in
> + * xfs_iomap_write_unwritten()
> + */
> + error = xfs_iomap_write_unwritten(ip, offset, size, false);
> break;
> default:
> ASSERT(!xfs_ioend_is_append(ioend) || ioend->io_append_trans);
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 350b6d43ba23..d4796c5a88fe 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -434,7 +434,6 @@ xfs_dio_write_end_io(
> struct inode *inode = file_inode(iocb->ki_filp);
> struct xfs_inode *ip = XFS_I(inode);
> loff_t offset = iocb->ki_pos;
> - bool update_size = false;
> int error = 0;
>
> trace_xfs_end_io_direct_write(ip, offset, size);
> @@ -445,6 +444,22 @@ xfs_dio_write_end_io(
> if (size <= 0)
> return size;
>
> + if (flags & IOMAP_DIO_COW) {
> + error = xfs_reflink_end_cow(ip, offset, size);
> + if (error)
> + return error;
> + }
So this should be ok, but without digging in the details I wonder
if we have proper tests for COWing the last block.
e.g. something like
write data from bytes 0 to 4000 to file a
clone file a to file b
write bytes 4000 to 4008 on file b
> @@ -900,6 +902,9 @@ xfs_iomap_write_unwritten(
> if (i_size > offset + count)
> i_size = offset + count;
>
> + if (update_isize && (i_size > i_size_read(inode)))
no need for the inner braces here.
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