[PATCH] safe_create_leading_directories: fix race that could give a false negative

[Steven Walter <stevenrwalter@gmail.com>]

If two processes are racing to create the same directory tree, they will
both see that the directory doesn't exist, both try to mkdir(), and one
of them will fail.  This is okay, as we only care that the directory
gets created.  So, we add a check for EEXIST from mkdir, and continue if
the directory now exists.
---
 sha1_file.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sha1_file.c b/sha1_file.c
index 40b2329..c7b7fec 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -123,6 +123,13 @@ int safe_create_leading_directories(char *path)
 			}
 		}
 		else if (mkdir(path, 0777)) {
+			if (errno == EEXIST) {
+				/* We could be racing with another process to
+				 * create the directory.  As long as the
+				 * directory gets created, we don't care. */
+				if (stat(path, &st) && S_ISDIR(st.st_mode))
+					continue;
+			}
 			*pos = '/';
 			return -1;
 		}
-- 
1.7.10.4