On Fri, Jan 26, 2018 at 01:06:52AM -0800, Christoph Hellwig wrote:
> On Tue, Jan 23, 2018 at 06:18:03PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > Before we share blocks between files, we need to break the pnfs leases
> > on the layout before we start slicing and dicing the block map.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > fs/xfs/xfs_reflink.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 47 insertions(+), 1 deletion(-)
> >
> >
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index 47aea2e..f89a725 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -1245,6 +1245,50 @@ xfs_reflink_remap_blocks(
> > }
> >
> > /*
> > + * Grab the exclusive iolock for a data copy from src to dest, making
> > + * sure to abide vfs locking order (lowest pointer value goes first) and
> > + * breaking the pnfs layout leases on dest before proceeding. The loop
> > + * is needed because we cannot call the blocking break_layout() with the
> > + * src iolock held, and therefore have to back out both locks.
> > + */
> > +static int
> > +xfs_iolock_two_inodes_and_break_layout(
> > + struct inode *src,
> > + struct inode *dest)
> > +{
> > + bool src_first = src < dest;
> > + bool src_last = src > dest;
>
> I find the double predicates here highly confusing.
>
> Also the code doesn't seem to handle the src == dest case as
> far as I can tell.
I guess they are confusing; when src == dest, src_first and src_last are
both false.
> > +retry:
> > + if (src_first) {
> > + inode_lock(src);
> > + inode_lock_nested(dest, I_MUTEX_NONDIR2);
> > + } else {
> > + inode_lock(dest);
> > + }
>
> Shouldn't this be replaced by a call to lock_two_nondirectories?
> Even if that holds both locks over the noon-blocking break_layout
> it makes things a lot simpler and only does an additional rountrip
> for the layouts outstanding slow path.
>
> > + error = break_layout(dest, false);
> > + if (error == -EWOULDBLOCK) {
> > + inode_unlock(dest);
> > + if (src_first)
> > + inode_unlock(src);
>
> unlock_two_nondirectories?
>
> > + error = break_layout(dest, true);
> > + if (error)
> > + return error;
> > + goto retry;
> > + } else if (error) {
>
> no need for an else after a goto.
>
> > + inode_unlock(dest);
> > + if (src_first)
> > + inode_unlock(src);
>
> unlock_two_nondirectories?
>
> Also seems like this could be simplified to:
>
> if (error) {
> unlock_two_nondirectories()
> if (error == -EWOULDBLOCK)
> goto retry;
> return error;
> }
>
> So I guess the whole thing could simply become something like:
>
> retry:
> lock_two_nondirectories(src, dest);
> error = break_layout(dest, false);
> if (error) {
> unlock_two_nondirectories(src, dest);
> if (error == -EWOULDBLOCK)
> goto retry;
> return error;
> }
>
> and could probably just be inlined into the caller..
Yeah, that's simpler... though at this point I'll have to put all this
into a new series having already pushed to for-next. :/
(Sorry, kinda overburdened with this week)
--D
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