Close the race on path ID allocation in xpt_bus_register() if two buses are

registered simultaneously. Due to topology unlock between the ID allocation
and the bus registration there is a chance that two buses may get the
same IDs. That is supposed reason of lock assertion panic in CAM during
initial bus scanning after new iscsid initiates two sessions same time.

Reported by:	trasz
Approved by:	re (glebus, marius)
MFC after:	2 weeks

1 files changed, 6 insertions, 9 deletions

diff --git a/sys/cam/cam_xpt.c b/sys/cam/cam_xpt.c
index 142195b..01025ff 100644
--- a/sys/cam/cam_xpt.c
+++ b/sys/cam/cam_xpt.c
@@ -2415,7 +2415,7 @@ xptsetasyncbusfunc(struct cam_eb *bus, void *arg)
 	struct ccb_setasync *csa = (struct ccb_setasync *)arg;
 
 	xpt_compile_path(&path, /*periph*/NULL,
-			 bus->sim->path_id,
+			 bus->path_id,
 			 CAM_TARGET_WILDCARD,
 			 CAM_LUN_WILDCARD);
 	xpt_setup_ccb(&cpi.ccb_h, &path, CAM_PRIORITY_NORMAL);
@@ -3840,13 +3840,8 @@ xpt_bus_register(struct cam_sim *sim, device_t parent, u_int32_t bus)
 		/* Couldn't satisfy request */
 		return (CAM_RESRC_UNAVAIL);
 	}
-	if (strcmp(sim->sim_name, "xpt") != 0) {
-		sim->path_id =
-		    xptpathid(sim->sim_name, sim->unit_number, sim->bus_id);
-	}
 
 	TAILQ_INIT(&new_bus->et_entries);
-	new_bus->path_id = sim->path_id;
 	cam_sim_hold(sim);
 	new_bus->sim = sim;
 	timevalclear(&new_bus->last_reset);
@@ -3855,6 +3850,8 @@ xpt_bus_register(struct cam_sim *sim, device_t parent, u_int32_t bus)
 	new_bus->generation = 0;
 
 	xpt_lock_buses();
+	sim->path_id = new_bus->path_id =
+	    xptpathid(sim->sim_name, sim->unit_number, sim->bus_id);
 	old_bus = TAILQ_FIRST(&xsoftc.xpt_busses);
 	while (old_bus != NULL
 	    && old_bus->path_id < new_bus->path_id)
@@ -3958,8 +3955,8 @@ xptnextfreepathid(void)
 	path_id_t pathid;
 	const char *strval;
 
+	mtx_assert(&xsoftc.xpt_topo_lock, MA_OWNED);
 	pathid = 0;
-	xpt_lock_buses();
 	bus = TAILQ_FIRST(&xsoftc.xpt_busses);
 retry:
 	/* Find an unoccupied pathid */
@@ -3968,7 +3965,6 @@ retry:
 			pathid++;
 		bus = TAILQ_NEXT(bus, links);
 	}
-	xpt_unlock_buses();
 
 	/*
 	 * Ensure that this pathid is not reserved for
@@ -3977,7 +3973,6 @@ retry:
 	if (resource_string_value("scbus", pathid, "at", &strval) == 0) {
 		++pathid;
 		/* Start the search over */
-		xpt_lock_buses();
 		goto retry;
 	}
 	return (pathid);
@@ -3993,6 +3988,8 @@ xptpathid(const char *sim_name, int sim_unit, int sim_bus)
 
 	pathid = CAM_XPT_PATH_ID;
 	snprintf(buf, sizeof(buf), "%s%d", sim_name, sim_unit);
+	if (strcmp(buf, "xpt0") == 0 && sim_bus == 0)
+		return (pathid);
 	i = 0;
 	while ((resource_find_match(&i, &dname, &dunit, "at", buf)) == 0) {
 		if (strcmp(dname, "scbus")) {