Re: [PATCH 02/11] xfs: only grab shared inode locks for source file during reflink

On Fri, Jan 26, 2018 at 04:07:41AM -0800, Christoph Hellwig wrote:

quoted

+xfs_lock_two_inodes_separately(
+	struct xfs_inode	*ip0,
+	uint			ip0_mode,
+	struct xfs_inode	*ip1,
+	uint			ip1_mode)

We only have 6 calls to xfs_lock_two_inodes in total, so just update
the signature to take two modes and be done with it.

Also how about mode1 and mode2 for the argument names?

quoted

 	lp = (xfs_log_item_t *)ip0->i_itemp;
 	if (lp && (lp->li_flags & XFS_LI_IN_AIL)) {
-		if (!xfs_ilock_nowait(ip1, xfs_lock_inumorder(lock_mode, 1))) {
-			xfs_iunlock(ip0, lock_mode);
+		if (!xfs_ilock_nowait(ip1, xfs_lock_inumorder(ip1_mode, 1))) {
+			xfs_iunlock(ip0, ip0_mode);
 			if ((++attempts % 5) == 0)
 				delay(1); /* Don't just spin the CPU */
 			goto again;
 		}
 	} else {
-		xfs_ilock(ip1, xfs_lock_inumorder(lock_mode, 1));
+		xfs_ilock(ip1, xfs_lock_inumorder(ip1_mode, 1));
 	}
 }

Not directly related to your patch, but the the nowait + retry
mess must go away.

Agree with the yuckiness; how often do we encounter that situation?

I think we need to move to the VFS locking conventions, that is
based on ancestors for directories (see lock_rename) and otherwise
based on the struct inode address as in lock_two_nondirectories.

I'd been wondering if the difference in locking conventions would ever
come to bite us...

quoted

      if (src_last)
-             inode_lock_nested(src, I_MUTEX_NONDIR2);
+             down_read_nested(&src->i_rwsem, I_MUTEX_NONDIR2);

Why is this not using inode_lock_nested any more?

Because inode_lock_nested calls down_write_nested, but I suppose I could
have simply added an inode_lock_shared_nested helper to make it more
consistent.

--D

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