5148 zvol's DKIOCFREE holds zfsdev_state_lock too long

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Paul Dagnelie <paul.dagnelie@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

usr/src/uts/common/fs/zfs/zvol.c

@@ -1781,8 +1781,8 @@ zvol_ioctl(dev_t dev, int cmd, intptr_t arg, int flag, cred_t *cr, int *rvalp)
 		 */
 		if (df.df_start >= zv->zv_volsize)
 			break;	/* No need to do anything... */
-		if (df.df_start + df.df_length > zv->zv_volsize)
-			df.df_length = DMU_OBJECT_END;
+
+		mutex_exit(&zfsdev_state_lock);
 
 		rl = zfs_range_lock(&zv->zv_znode, df.df_start, df.df_length,
 		    RL_WRITER);
@@ -1821,7 +1821,7 @@ zvol_ioctl(dev_t dev, int cmd, intptr_t arg, int flag, cred_t *cr, int *rvalp)
 				    dmu_objset_pool(zv->zv_objset), 0);
 			}
 		}
-		break;
+		return (error);
 	}
 
 	default: