Fix vdev_open_child() race on updating vdev_parent->vdev_nonrot

Updating vd->vdev_parent->vdev_nonrot in vdev_open_child()
is a race when vdev_open_child is called for many children
from a task queue.

vdev_open_child() is only called by vdev_open_children(), let
the latter update the parent vdev_nonrot member.  The update
was already there, so done twice previously.  Thus using the
same logic at the end in vdev_open_children() to update
vdev_nonrot, either we are vdev_uses_zvols() or not.

Reviewed-by: Richard Elling <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Haakan T Johansson <[email protected]>
Closes #5162 

1 files changed, 11 insertions, 14 deletions

diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index dcf56d8df..104db3d15 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -1124,7 +1124,6 @@ vdev_open_child(void *arg)
 	vd->vdev_open_thread = curthread;
 	vd->vdev_open_error = vdev_open(vd);
 	vd->vdev_open_thread = NULL;
-	vd->vdev_parent->vdev_nonrot &= vd->vdev_nonrot;
 }
 
 static boolean_t
@@ -1151,29 +1150,27 @@ vdev_open_children(vdev_t *vd)
 	int children = vd->vdev_children;
 	int c;
 
-	vd->vdev_nonrot = B_TRUE;
-
 	/*
 	 * in order to handle pools on top of zvols, do the opens
 	 * in a single thread so that the same thread holds the
 	 * spa_namespace_lock
 	 */
 	if (vdev_uses_zvols(vd)) {
-		for (c = 0; c < children; c++) {
+		for (c = 0; c < children; c++)
 			vd->vdev_child[c]->vdev_open_error =
 			    vdev_open(vd->vdev_child[c]);
-			vd->vdev_nonrot &= vd->vdev_child[c]->vdev_nonrot;
-		}
-		return;
-	}
-	tq = taskq_create("vdev_open", children, minclsyspri,
-	    children, children, TASKQ_PREPOPULATE);
+	} else {
+		tq = taskq_create("vdev_open", children, minclsyspri,
+		    children, children, TASKQ_PREPOPULATE);
 
-	for (c = 0; c < children; c++)
-		VERIFY(taskq_dispatch(tq, vdev_open_child, vd->vdev_child[c],
-		    TQ_SLEEP) != 0);
+		for (c = 0; c < children; c++)
+			VERIFY(taskq_dispatch(tq, vdev_open_child,
+			    vd->vdev_child[c], TQ_SLEEP) != 0);
 
-	taskq_destroy(tq);
+		taskq_destroy(tq);
+	}
+
+	vd->vdev_nonrot = B_TRUE;
 
 	for (c = 0; c < children; c++)
 		vd->vdev_nonrot &= vd->vdev_child[c]->vdev_nonrot;