On Thu, Sep 21, 2017 at 08:07:10AM -0400, Brian Foster wrote:
> 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
> >
>
> Looks pretty good, just a few comment/whitespace nits...
>
> > 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()
> > + */
>
> The more I think about this, the less applicable the granularity seems
> to be (sorry :P). It seems rather broken if writeback were to affect
> isize in general. Perhaps just the following?
>
> /* writeback should never update isize */
Sure :)
>
> > + 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;
> > + }
> > +
> > + /*
> > + * Deal with IOMAP_DIO_UNWRITTEN case before check & update in-core
> > + * inode size, we do it only after converting the unwritten extents to
> > + * real allocations in xfs_iomap_write_write_unwritten() (by passing
> > + * 'true' as the last argument to it), otherwise a racing direct read
> > + * could see the new size thus read zeros because of unwritten extents.
> > + */
>
> /*
> * Unwritten conversion updates the in-core isize after extent
> * conversion but before updating the on-disk size. Updating isize any
> * earlier allows a racing dio read to find unwritten extents before
> * they are converted.
> */
I'll just copy native English speaker's comments :)
>
> > + if (flags & IOMAP_DIO_UNWRITTEN)
> > + return xfs_iomap_write_unwritten(ip, offset, size, true);
> > +
> > /*
> > * We need to update the in-core inode size here so that we don't end up
> > * with the on-disk inode size being outside the in-core inode size. We
> > @@ -459,20 +474,11 @@ xfs_dio_write_end_io(
> > spin_lock(&ip->i_flags_lock);
> > if (offset + size > i_size_read(inode)) {
> > i_size_write(inode, offset + size);
> > - update_size = true;
> > - }
> > - spin_unlock(&ip->i_flags_lock);
> > -
> > - if (flags & IOMAP_DIO_COW) {
> > - error = xfs_reflink_end_cow(ip, offset, size);
> > - if (error)
> > - return error;
> > - }
> > -
> > - if (flags & IOMAP_DIO_UNWRITTEN)
> > - error = xfs_iomap_write_unwritten(ip, offset, size);
> > - else if (update_size)
> > + spin_unlock(&ip->i_flags_lock);
> > error = xfs_setfilesize(ip, offset, size);
> > + } else {
> > + spin_unlock(&ip->i_flags_lock);
> > + }
> >
> > return error;
> > }
> > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > index a1909bc064e9..90dc551a8621 100644
> > --- a/fs/xfs/xfs_iomap.c
> > +++ b/fs/xfs/xfs_iomap.c
> > @@ -829,7 +829,8 @@ int
> > xfs_iomap_write_unwritten(
> > xfs_inode_t *ip,
> > xfs_off_t offset,
> > - xfs_off_t count)
> > + xfs_off_t count,
> > + bool update_isize)
> > {
> > xfs_mount_t *mp = ip->i_mount;
> > xfs_fileoff_t offset_fsb;
> > @@ -840,6 +841,7 @@ xfs_iomap_write_unwritten(
> > xfs_trans_t *tp;
> > xfs_bmbt_irec_t imap;
> > struct xfs_defer_ops dfops;
> > + struct inode *inode = VFS_I(ip);
> > xfs_fsize_t i_size;
> > uint resblks;
> > int error;
> > @@ -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)))
> > + i_size_write(inode, i_size);
> > +
>
> We could probably kill the blank lines around the above hunk.
Will do.
>
> With those minor fixups:
>
> Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
>
> Thanks for taking care of this!
Thanks a lot for your suggestions and reviews!
Eryu
>
> > i_size = xfs_new_eof(ip, i_size);
> > if (i_size) {
> > ip->i_d.di_size = i_size;
> > diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
> > index 00db3ecea084..ee535065c5d0 100644
> > --- a/fs/xfs/xfs_iomap.h
> > +++ b/fs/xfs/xfs_iomap.h
> > @@ -27,7 +27,7 @@ int xfs_iomap_write_direct(struct xfs_inode *, xfs_off_t, size_t,
> > struct xfs_bmbt_irec *, int);
> > int xfs_iomap_write_allocate(struct xfs_inode *, int, xfs_off_t,
> > struct xfs_bmbt_irec *);
> > -int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t);
> > +int xfs_iomap_write_unwritten(struct xfs_inode *, xfs_off_t, xfs_off_t, bool);
> >
> > void xfs_bmbt_to_iomap(struct xfs_inode *, struct iomap *,
> > struct xfs_bmbt_irec *);
> > diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
> > index 2f2dc3c09ad0..4246876df7b7 100644
> > --- a/fs/xfs/xfs_pnfs.c
> > +++ b/fs/xfs/xfs_pnfs.c
> > @@ -274,7 +274,7 @@ xfs_fs_commit_blocks(
> > (end - 1) >> PAGE_SHIFT);
> > WARN_ON_ONCE(error);
> >
> > - error = xfs_iomap_write_unwritten(ip, start, length);
> > + error = xfs_iomap_write_unwritten(ip, start, length, false);
> > if (error)
> > goto out_drop_iolock;
> > }
> > --
> > 2.13.5
> >
> > --
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