[release-branch.go1.25] os: fix Root.MkdirAll to handle race of directory creation

No tests were added, because in order to reproduce, the directory would
have to be created precisely between the rootOpenDir and mkdirat calls,
which is impossible to do in a test.

Fixes #75116

Change-Id: I6f86a5b33c87452c35728318eaf2169a7534ef37
Reviewed-on: https://go-review.googlesource.com/c/go/+/698215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Sean Liao <sean@liao.dev>
(cherry picked from commit a076f497577605e4cf0e20c147711e03dee7b2c3)
Reviewed-on: https://go-review.googlesource.com/c/go/+/700655
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

diff --git a/src/os/root_openat.go b/src/os/root_openat.go
index e433bd5093fdb014f42a4fb487ac58019fa0b20a..83bde5ef14160d08763b017283351251e355b5f1 100644 (file)
--- a/src/os/root_openat.go
+++ b/src/os/root_openat.go
@@ -131,7 +131,9 @@ func rootMkdirAll(r *Root, fullname string, perm FileMode) error {
                        if try > 0 || !IsNotExist(err) {
                                return 0, &PathError{Op: "openat", Err: err}
                        }
-                       if err := mkdirat(parent, name, perm); err != nil {
+                       // Try again on EEXIST, because the directory may have been created
+                       // by another process or thread between the rootOpenDir and mkdirat calls.
+                       if err := mkdirat(parent, name, perm); err != nil && err != syscall.EEXIST {
                                return 0, &PathError{Op: "mkdirat", Err: err}
                        }
                }