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:

quoted

From: Darrick J. Wong <redacted>

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 <redacted>
---
 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.

quoted

+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.

quoted

+	error = break_layout(dest, false);
+	if (error == -EWOULDBLOCK) {
+		inode_unlock(dest);
+		if (src_first)
+			inode_unlock(src);

unlock_two_nondirectories?

quoted

+		error = break_layout(dest, true);
+		if (error)
+			return error;
+		goto retry;
+	} else if (error) {

no need for an else after a goto.

quoted

+		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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