Re: [PATCH V4 03/10] xfs: Check for extent overflow when punching a hole

Chandan Babu R
2020-09-19T09:42:36Z

On Friday 18 September 2020 9:24:52 PM IST Darrick J. Wong wrote:
> On Fri, Sep 18, 2020 at 03:17:52PM +0530, Chandan Babu R wrote:
> > The extent mapping the file offset at which a hole has to be
> > inserted will be split into two extents causing extent count to
> > increase by 1.
> >
> > Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> > ---
> > fs/xfs/libxfs/xfs_inode_fork.h | 7 +++++++
> > fs/xfs/xfs_bmap_item.c | 5 +++++
> > fs/xfs/xfs_bmap_util.c | 10 ++++++++++
> > 3 files changed, 22 insertions(+)
> >
> > diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> > index 7fc2b129a2e7..bcac769a7df6 100644
> > --- a/fs/xfs/libxfs/xfs_inode_fork.h
> > +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> > @@ -40,6 +40,13 @@ struct xfs_ifork {
> > */
> > #define XFS_IEXT_ADD_NOSPLIT_CNT (1)
> >
> > +/*
> > + * Punching out an extent from the middle of an existing extent can cause the
> > + * extent count to increase by 1.
> > + * i.e. | Old extent | Hole | Old extent |
> > + */
> > +#define XFS_IEXT_PUNCH_HOLE_CNT (1)
> > +
> > /*
> > * Fork handling.
> > */
> > diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> > index ec3691372e7c..5c7d08da8ff1 100644
> > --- a/fs/xfs/xfs_bmap_item.c
> > +++ b/fs/xfs/xfs_bmap_item.c
> > @@ -519,6 +519,11 @@ xfs_bui_item_recover(
> > }
> > xfs_trans_ijoin(tp, ip, 0);
> >
> > + error = xfs_iext_count_may_overflow(ip, whichfork,
> > + XFS_IEXT_PUNCH_HOLE_CNT);
>
> I think this ought to be XFS_IEXT_ADD_NOSPLIT_CNT if bui_type is
> XFS_BMAP_MAP and XFS_IEXT_PUNCH_HOLE_CNT if XFS_BMAP_UNMAP.

You are right. I will include this change in the next version.

>
> Whoever created the BUI should have called xfs_iext_count_may_overflow
> before logging the BUI (and hence this should never occur) but it does
> pay to be careful. :)
>
> The rest of the logic in the patch looks ok.
>
> --D
>
> > + if (error)
> > + goto err_inode;
> > +
> > count = bmap->me_len;
> > error = xfs_trans_log_finish_bmap_update(tp, budp, type, ip, whichfork,
> > bmap->me_startoff, bmap->me_startblock, &count, state);
> > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> > index dcd6e61df711..0776abd0103c 100644
> > --- a/fs/xfs/xfs_bmap_util.c
> > +++ b/fs/xfs/xfs_bmap_util.c
> > @@ -891,6 +891,11 @@ xfs_unmap_extent(
> >
> > xfs_trans_ijoin(tp, ip, 0);
> >
> > + error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
> > + XFS_IEXT_PUNCH_HOLE_CNT);
> > + if (error)
> > + goto out_trans_cancel;
> > +
> > error = xfs_bunmapi(tp, ip, startoffset_fsb, len_fsb, 0, 2, done);
> > if (error)
> > goto out_trans_cancel;
> > @@ -1176,6 +1181,11 @@ xfs_insert_file_space(
> > xfs_ilock(ip, XFS_ILOCK_EXCL);
> > xfs_trans_ijoin(tp, ip, 0);
> >
> > + error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
> > + XFS_IEXT_PUNCH_HOLE_CNT);
> > + if (error)
> > + goto out_trans_cancel;
> > +
> > /*
> > * The extent shifting code works on extent granularity. So, if stop_fsb
> > * is not the starting block of extent, we need to split the extent at
>

--
chandan