diff --git a/hgext3rd/undo.py b/hgext3rd/undo.py
--- a/hgext3rd/undo.py
+++ b/hgext3rd/undo.py
@@ -21,6 +21,7 @@
     smartset,
     transaction,
     util,
+    vfs as vfsmod,
 )
 
 from mercurial.node import (
@@ -58,6 +59,19 @@
 
 # Write: Log control
 
+def undovfs(repo):
+    """return vfs used for writing undo logs
+
+    Avoid using repo.svfs directly since it has extra locking checks that are
+    not applicable to us. We have our own locking and transaction control that
+    do not dependent on repo transaction or locks.
+    """
+    if not util.safehasattr(repo, '_undovfs'):
+        vfs = vfsmod.vfs(repo.svfs.join('undolog'))
+        vfs.makedirs()
+        repo._undovfs = vfs
+    return repo._undovfs
+
 def safelog(repo, command):
     '''boilerplate for log command
 
@@ -73,8 +87,7 @@
         # allows running command during other commands when
         # otherwise legal.  Could cause weird undolog states,
         # which gap handling generally covers.
-        with lockmod.lock(repo.vfs, "undologlock",
-                          desc="undolog"):
+        with lockmod.lock(undovfs(repo), "undologlock", desc="undolog"):
             # developer config: undo._duringundologlock
             if repo.ui.configbool('undo', '_duringundologlock'):
                 repo.hook("duringundologlock")
@@ -93,8 +106,8 @@
     # executed, doesn't check repo locks, doesn't check
     # abandoned tr's (since we only record info) and doesn't
     # do any tag handling
-    vfsmap = {'plain': repo.vfs}
-    tr = transaction.transaction(repo.ui.warn, repo.svfs, vfsmap,
+    vfsmap = {'plain': undovfs(repo)}
+    tr = transaction.transaction(repo.ui.warn, undovfs(repo), vfsmap,
                                  "_undojournal", "_undolog")
     return tr
 
@@ -137,7 +150,6 @@
         raise error.ProgrammingError
     # the transaction code doesn't work with vfs
     # specifically, repo.recover() assumes svfs?
-    repo.svfs.makedirs('undolog')
     rlog = _getrevlog(repo, name)
     node = rlog.addrevision(revstring, tr, 1, nullid, nullid)
     return hex(node)
@@ -315,5 +327,4 @@
     return len(rlog) - 1 - indexorreverseindex
 
 def _getrevlog(repo, filename):
-    path = 'undolog/' + filename
-    return revlog.revlog(repo.svfs, path)
+    return revlog.revlog(undovfs(repo), filename)