sd: flush cache when closing writable FD

[Stefan Fritsch]

Don't skip the cache flush until the last opening of the device is
closed. Otherwise, when umounting a writable partition while a different
partition is still mounted read-only, the necessary disk flush may be
delayed for a very long time.


diff --git sys/scsi/sd.c sys/scsi/sd.c
index 4cd0e4d13bd..37135af78a1 100644
--- sys/scsi/sd.c
+++ sys/scsi/sd.c
@@ -511,10 +511,11 @@ sdclose(dev_t dev, int flag, int fmt, struct proc *p)
 
        disk_closepart(&sc->sc_dk, part, fmt);
 
-       if (sc->sc_dk.dk_openmask == 0) {
-               if ((sc->flags & SDF_DIRTY) != 0)
-                       sd_flush(sc, 0);
+       if (((flag & FWRITE) != 0 || sc->sc_dk.dk_openmask == 0) &&
+           (sc->flags & SDF_DIRTY) != 0)
+               sd_flush(sc, 0);
 
+       if (sc->sc_dk.dk_openmask == 0) {
                if (sc->flags & SDF_DYING) {
                        error = ENXIO;
                        goto die;