[PATCH] Documentation: fs: fix directory locking proofs

[Mo Zou <lostzoumo@gmail.com>]

Commit 28eceeda130f ("fs: Lock moved directories") acquires locks also for
directories when they are moved and updates the deadlock-freedom proof
to claim "a linear ordering of the objects - A < B iff (A is an ancestor
of B) or (B is an ancestor of A and ptr(A) < ptr(B))". This claim,
however, is not correct. Because cross-directory rename may acquire two
parents (old parent and new parent) and two child directories (source
and target) and the ordering between old parent and target (or new parent
and source) may not fall into the above cases, i.e. ptr(old parent) <
ptr(target) may not hold. We should revert to previous description that
"at any moment we have a partial ordering of the objects - A < B iff A is
an ancestor of B".

Signed-off-by: Mo Zou <lostzoumo@gmail.com>
---
 Documentation/filesystems/directory-locking.rst | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/directory-locking.rst b/Documentation/filesystems/directory-locking.rst
index dccd61c7c5c3..5b26ecd9f0db 100644
--- a/Documentation/filesystems/directory-locking.rst
+++ b/Documentation/filesystems/directory-locking.rst
@@ -67,9 +67,8 @@ If no directory is its own ancestor, the scheme above is deadlock-free.
 
 Proof:
 
-	First of all, at any moment we have a linear ordering of the
-	objects - A < B iff (A is an ancestor of B) or (B is not an ancestor
-        of A and ptr(A) < ptr(B)).
+	First of all, at any moment we have a partial ordering of the
+	objects - A < B iff A is an ancestor of B.
 
 	That ordering can change.  However, the following is true:
 
-- 
2.30.1 (Apple Git-130)