mitigate against mpii device attachment racing with mountroot

mpii devices get attached by processing sas discovery events after
threads are running, but if you have a lean (in terms of devices)
and fast machine, these events might run after mountroot.

this change has mpii use config_pending_incr() before it attaches
scsibus, and runs config_pending_decr() after the first scan of the
bus is complete.

to make sure config_pending_decr() is run after the scsi attach/detach
events are processed, the MPII_EVENT_SAS_DISCOVERY events are
deferred to the same context that the MPII_EVENT_SAS_TOPOLOGY_CHANGE_LIST
events run in.

ok jmatthew@

1 files changed, 42 insertions, 12 deletions

diff --git a/sys/dev/pci/mpii.c b/sys/dev/pci/mpii.c
index 90a24e9dd14..fc5e5ae9fc8 100644
--- a/sys/dev/pci/mpii.c
+++ b/sys/dev/pci/mpii.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mpii.c,v 1.105 2016/09/14 01:14:54 jmatthew Exp $	*/
+/*	$OpenBSD: mpii.c,v 1.106 2016/10/21 05:38:53 dlg Exp $	*/
 /*
  * Copyright (c) 2010, 2012 Mike Belopuhov
  * Copyright (c) 2009 James Giannoules
@@ -164,6 +164,7 @@ struct mpii_softc {
 	int			sc_flags;
 #define MPII_F_RAID		(1<<1)
 #define MPII_F_SAS3		(1<<2)
+#define MPII_F_CONFIG_PENDING	(1<<3)
 
 	struct scsibus_softc	*sc_scsibus;
 
@@ -344,6 +345,8 @@ void		mpii_event_done(struct mpii_softc *, struct mpii_rcb *);
 void		mpii_event_sas(void *);
 void		mpii_event_raid(struct mpii_softc *,
 		    struct mpii_msg_event_reply *);
+void		mpii_event_discovery(struct mpii_softc *,
+		    struct mpii_msg_event_reply *);
 
 void		mpii_sas_remove_device(struct mpii_softc *, u_int16_t);
 
@@ -590,6 +593,10 @@ mpii_attach(struct device *parent, struct device *self, void *aux)
 	if (sc->sc_ih == NULL)
 		goto free_devs;
 
+	/* force autoconf to wait for the first sas discovery to complete */
+	SET(sc->sc_flags, MPII_F_CONFIG_PENDING);
+	config_pending_incr();
+
 	/* config_found() returns the scsibus attached to us */
 	sc->sc_scsibus = (struct scsibus_softc *) config_found(&sc->sc_dev,
 	    &saa, scsiprint);
@@ -1795,6 +1802,19 @@ mpii_event_sas(void *xsc)
 		task_add(systq, &sc->sc_evt_sas_task);
 
 	enp = (struct mpii_msg_event_reply *)rcb->rcb_reply;
+	switch (lemtoh16(&enp->event)) {
+	case MPII_EVENT_SAS_DISCOVERY:
+		mpii_event_discovery(sc, enp);
+		goto done;
+	case MPII_EVENT_SAS_TOPOLOGY_CHANGE_LIST:
+		/* handle below */
+		break;
+	default:
+		panic("%s: unexpected event %#x in sas event queue",
+		    DEVNAME(sc), lemtoh16(&enp->event));
+		/* NOTREACHED */
+	}
+
 	tcl = (struct mpii_evt_sas_tcl *)(enp + 1);
 	pe = (struct mpii_evt_phy_entry *)(tcl + 1);
 
@@ -1846,10 +1866,30 @@ mpii_event_sas(void *xsc)
 		}
 	}
 
+done:
 	mpii_event_done(sc, rcb);
 }
 
 void
+mpii_event_discovery(struct mpii_softc *sc, struct mpii_msg_event_reply *enp)
+{
+	struct mpii_evt_sas_discovery *esd =
+	    (struct mpii_evt_sas_discovery *)(enp + 1);
+
+	if (esd->reason_code == MPII_EVENT_SAS_DISC_REASON_CODE_COMPLETED) {
+		if (esd->discovery_status != 0) {
+			printf("%s: sas discovery completed with status %#x\n",
+			    DEVNAME(sc), esd->discovery_status);
+		}
+
+		if (ISSET(sc->sc_flags, MPII_F_CONFIG_PENDING)) {
+			CLR(sc->sc_flags, MPII_F_CONFIG_PENDING);
+			config_pending_decr();
+		}
+	}
+}
+
+void
 mpii_event_process(struct mpii_softc *sc, struct mpii_rcb *rcb)
 {
 	struct mpii_msg_event_reply		*enp;
@@ -1863,17 +1903,7 @@ mpii_event_process(struct mpii_softc *sc, struct mpii_rcb *rcb)
 	case MPII_EVENT_EVENT_CHANGE:
 		/* should be properly ignored */
 		break;
-	case MPII_EVENT_SAS_DISCOVERY: {
-		struct mpii_evt_sas_discovery	*esd =
-		    (struct mpii_evt_sas_discovery *)(enp + 1);
-
-		if (esd->reason_code ==
-		    MPII_EVENT_SAS_DISC_REASON_CODE_COMPLETED &&
-		    esd->discovery_status != 0)
-			printf("%s: sas discovery completed with status %#x\n",
-			    DEVNAME(sc), esd->discovery_status);
-		}
-		break;
+	case MPII_EVENT_SAS_DISCOVERY:
 	case MPII_EVENT_SAS_TOPOLOGY_CHANGE_LIST:
 		mtx_enter(&sc->sc_evt_sas_mtx);
 		SIMPLEQ_INSERT_TAIL(&sc->sc_evt_sas_queue, rcb, rcb_link);