helper/seccomp: eliminate data race on pfd

Turns out the doc comment on os.File was lying about its methods being safe for concurrent use. The race detector picked up a data race from concurrent use of Fd and Close.

This change eliminates that by calling Fd in the prepare routine.

Signed-off-by: Ophestra <cat@gensokyo.uk>

helper/seccomp/export.go

@@ -28,7 +28,7 @@ func (e *exporter) prepare() error {
 		}
 
 		ec := make(chan error, 1)
-		go func() { ec <- exportFilter(e.w.Fd(), e.opts); close(ec); _ = e.closeWrite() }()
+		go func(fd uintptr) { ec <- exportFilter(fd, e.opts); close(ec); _ = e.closeWrite() }(e.w.Fd())
 		e.exportErr = ec
 		runtime.SetFinalizer(e, (*exporter).closeWrite)
 	})