[Midnightbsd-cvs] src [8214] trunk/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c: zfs: allow a zvol to be used as a pool vdev, again

[laffer1 at midnightbsd.org]

Revision: 8214
          http://svnweb.midnightbsd.org/src/?rev=8214
Author:   laffer1
Date:     2016-09-17 16:21:30 -0400 (Sat, 17 Sep 2016)
Log Message:
-----------
zfs: allow a zvol to be used as a pool vdev, again

Modified Paths:
--------------
    trunk/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c

Modified: trunk/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c
===================================================================
--- trunk/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c	2016-09-17 20:21:07 UTC (rev 8213)
+++ trunk/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c	2016-09-17 20:21:30 UTC (rev 8214)
@@ -875,20 +875,28 @@
 {
 	zvol_state_t *zv;
 	int err = 0;
+	boolean_t locked = B_FALSE;
 
-	if (MUTEX_HELD(&spa_namespace_lock)) {
-		/*
-		 * If the spa_namespace_lock is being held, it means that ZFS
-		 * is trying to open ZVOL as its VDEV. This is not supported.
-		 */
-		return (EOPNOTSUPP);
+	/*
+	 * Protect against recursively entering spa_namespace_lock
+	 * when spa_open() is used for a pool on a (local) ZVOL(s).
+	 * This is needed since we replaced upstream zfsdev_state_lock
+	 * with spa_namespace_lock in the ZVOL code.
+	 * We are using the same trick as spa_open().
+	 * Note that calls in zvol_first_open which need to resolve
+	 * pool name to a spa object will enter spa_open()
+	 * recursively, but that function already has all the
+	 * necessary protection.
+	 */
+	if (!MUTEX_HELD(&spa_namespace_lock)) {
+		mutex_enter(&spa_namespace_lock);
+		locked = B_TRUE;
 	}
 
-	mutex_enter(&spa_namespace_lock);
-
 	zv = pp->private;
 	if (zv == NULL) {
-		mutex_exit(&spa_namespace_lock);
+		if (locked)
+			mutex_exit(&spa_namespace_lock);
 		return (ENXIO);
 	}
 
@@ -895,7 +903,8 @@
 	if (zv->zv_total_opens == 0)
 		err = zvol_first_open(zv);
 	if (err) {
-		mutex_exit(&spa_namespace_lock);
+		if (locked)
+			mutex_exit(&spa_namespace_lock);
 		return (err);
 	}
 	if ((flag & FWRITE) && (zv->zv_flags & ZVOL_RDONLY)) {
@@ -917,13 +926,15 @@
 #endif
 
 	zv->zv_total_opens += count;
-	mutex_exit(&spa_namespace_lock);
+	if (locked)
+		mutex_exit(&spa_namespace_lock);
 
 	return (err);
 out:
 	if (zv->zv_total_opens == 0)
 		zvol_last_close(zv);
-	mutex_exit(&spa_namespace_lock);
+	if (locked)
+		mutex_exit(&spa_namespace_lock);
 	return (err);
 }
 
@@ -933,12 +944,18 @@
 {
 	zvol_state_t *zv;
 	int error = 0;
+	boolean_t locked = B_FALSE;
 
-	mutex_enter(&spa_namespace_lock);
+	/* See comment in zvol_open(). */
+	if (!MUTEX_HELD(&spa_namespace_lock)) {
+		mutex_enter(&spa_namespace_lock);
+		locked = B_TRUE;
+	}
 
 	zv = pp->private;
 	if (zv == NULL) {
-		mutex_exit(&spa_namespace_lock);
+		if (locked)
+			mutex_exit(&spa_namespace_lock);
 		return (ENXIO);
 	}
 
@@ -961,7 +978,8 @@
 	if (zv->zv_total_opens == 0)
 		zvol_last_close(zv);
 
-	mutex_exit(&spa_namespace_lock);
+	if (locked)
+		mutex_exit(&spa_namespace_lock);
 	return (error);
 }