diff -r 770e1352e9f9 -r 90e564882f07 mercurial/utils/procutil.py
--- a/mercurial/utils/procutil.py	Mon Apr 18 20:45:38 2022 -0700
+++ b/mercurial/utils/procutil.py	Wed Apr 13 14:46:22 2022 -0400
@@ -112,7 +112,9 @@
         total_to_write = len(s)
         total_written = 0
         while total_written < total_to_write:
-            total_written += write1(m[total_written:])
+            c = write1(m[total_written:])
+            if c:
+                total_written += c
         return total_written