Use long holds in zvol_set_volsize()

Under Linux the zvol_set_volsize() function was originally written
to use dmu_objset_hold()/dmu_objset_rele().  Subsequently, the
dmu_objset_own()/dmu_objset_disown() interfaces were added but
the ZVOL code wasn't updated to take advantage of them.

This was never an issue but after the dsl_pool_config changes
the code now takes the config lock twice.  The cleanest solution
is to shift to using dmu_objset_own() which takes a long hold
on the dataset and does not hold the dsl pool lock.

This patch also slightly restructures the existing code such
that it more closely resembles the upstream Illumos code.

Signed-off-by: Ned Bass <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#2039

module/zfs/zvol.c

@@ -231,6 +231,31 @@ zvol_get_stats(objset_t *os, nvlist_t *nv)
 	return (SET_ERROR(error));
 }
 
+static void
+zvol_size_changed(zvol_state_t *zv, uint64_t volsize)
+{
+	struct block_device *bdev;
+
+	bdev = bdget_disk(zv->zv_disk, 0);
+	if (bdev == NULL)
+		return;
+/*
+ * 2.6.28 API change
+ * Added check_disk_size_change() helper function.
+ */
+#ifdef HAVE_CHECK_DISK_SIZE_CHANGE
+	set_capacity(zv->zv_disk, volsize >> 9);
+	zv->zv_volsize = volsize;
+	check_disk_size_change(zv->zv_disk, bdev);
+#else
+	zv->zv_volsize = volsize;
+	zv->zv_changed = 1;
+	(void) check_disk_change(bdev);
+#endif /* HAVE_CHECK_DISK_SIZE_CHANGE */
+
+	bdput(bdev);
+}
+
 /*
  * Sanity check volume size.
  */
@@ -254,9 +279,8 @@ zvol_check_volsize(uint64_t volsize, uint64_t blocksize)
  * Ensure the zap is flushed then inform the VFS of the capacity change.
  */
 static int
-zvol_update_volsize(zvol_state_t *zv, uint64_t volsize, objset_t *os)
+zvol_update_volsize(uint64_t volsize, objset_t *os)
 {
-	struct block_device *bdev;
 	dmu_tx_t *tx;
 	int error;
 
@@ -274,32 +298,23 @@ zvol_update_volsize(zvol_state_t *zv, uint64_t volsize, objset_t *os)
 	    &volsize, tx);
 	dmu_tx_commit(tx);
 
-	if (error)
-		return (SET_ERROR(error));
+	if (error == 0)
+		error = dmu_free_long_range(os,
+		    ZVOL_OBJ, volsize, DMU_OBJECT_END);
 
-	error = dmu_free_long_range(os,
-	    ZVOL_OBJ, volsize, DMU_OBJECT_END);
-	if (error)
-		return (SET_ERROR(error));
+	return (error);
+}
 
-	bdev = bdget_disk(zv->zv_disk, 0);
-	if (!bdev)
-		return (SET_ERROR(EIO));
-/*
- * 2.6.28 API change
- * Added check_disk_size_change() helper function.
- */
-#ifdef HAVE_CHECK_DISK_SIZE_CHANGE
-	set_capacity(zv->zv_disk, volsize >> 9);
-	zv->zv_volsize = volsize;
-	check_disk_size_change(zv->zv_disk, bdev);
-#else
-	zv->zv_volsize = volsize;
-	zv->zv_changed = 1;
-	(void) check_disk_change(bdev);
-#endif /* HAVE_CHECK_DISK_SIZE_CHANGE */
+static int
+zvol_update_live_volsize(zvol_state_t *zv, uint64_t volsize)
+{
+	zvol_size_changed(zv, volsize);
 
-	bdput(bdev);
+	/*
+	 * We should post a event here describing the expansion.  However,
+	 * the zfs_ereport_post() interface doesn't nicely support posting
+	 * events for zvols, it assumes events relate to vdevs or zios.
+	 */
 
 	return (0);
 }
@@ -310,11 +325,12 @@ zvol_update_volsize(zvol_state_t *zv, uint64_t volsize, objset_t *os)
 int
 zvol_set_volsize(const char *name, uint64_t volsize)
 {
-	zvol_state_t *zv;
-	dmu_object_info_t *doi;
+	zvol_state_t *zv = NULL;
 	objset_t *os = NULL;
-	uint64_t readonly;
 	int error;
+	dmu_object_info_t *doi;
+	uint64_t readonly;
+	boolean_t owned = B_FALSE;
 
 	error = dsl_prop_get_integer(name,
 	    zfs_prop_to_name(ZFS_PROP_READONLY), &readonly, NULL);
@@ -324,44 +340,40 @@ zvol_set_volsize(const char *name, uint64_t volsize)
 		return (SET_ERROR(EROFS));
 
 	mutex_enter(&zvol_state_lock);
-
 	zv = zvol_find_by_name(name);
-	if (zv == NULL) {
-		error = SET_ERROR(ENXIO);
-		goto out;
+
+	if (zv == NULL || zv->zv_objset == NULL) {
+		if ((error = dmu_objset_own(name, DMU_OST_ZVOL, B_FALSE,
+		    FTAG, &os)) != 0) {
+			mutex_exit(&zvol_state_lock);
+			return (SET_ERROR(error));
+		}
+		owned = B_TRUE;
+		if (zv != NULL)
+			zv->zv_objset = os;
+	} else {
+		os = zv->zv_objset;
 	}
 
 	doi = kmem_alloc(sizeof (dmu_object_info_t), KM_SLEEP);
 
-	error = dmu_objset_hold(name, FTAG, &os);
-	if (error)
-		goto out_doi;
-
 	if ((error = dmu_object_info(os, ZVOL_OBJ, doi)) ||
 	    (error = zvol_check_volsize(volsize, doi->doi_data_block_size)))
-		goto out_doi;
-
-	VERIFY(dsl_prop_get_integer(name, "readonly", &readonly, NULL) == 0);
-	if (readonly) {
-		error = SET_ERROR(EROFS);
-		goto out_doi;
-	}
-
-	if (zv->zv_flags & ZVOL_RDONLY) {
-		error = SET_ERROR(EROFS);
-		goto out_doi;
-	}
+		goto out;
 
-	error = zvol_update_volsize(zv, volsize, os);
-out_doi:
+	error = zvol_update_volsize(volsize, os);
 	kmem_free(doi, sizeof (dmu_object_info_t));
-out:
-	if (os)
-		dmu_objset_rele(os, FTAG);
 
+	if (error == 0 && zv != NULL)
+		error = zvol_update_live_volsize(zv, volsize);
+out:
+	if (owned) {
+		dmu_objset_disown(os, FTAG);
+		if (zv != NULL)
+			zv->zv_objset = NULL;
+	}
 	mutex_exit(&zvol_state_lock);
-
-	return (SET_ERROR(error));
+	return (error);
 }
 
 /*