Re-work management of the auto trim taskq...

... and related locking

Don't take the spa_auto_trim_lock in the sync path: The auto trim taskq
is now stopped and started in response to changes in the "autotrim"
property asynchronously by the spa async task.  If the spa_auto-trim_lock
is taken in the sync task, the system can deadlock
as follows:

	Non-sync context task: Acquires spa_auto_trim_lock via
	    spa_vdev_enter() or some other path.
	Sync task: syncing a change to the "autotrim" property attempts
	    to take spa_auto_trim_lock and blocks.
	Non-sync context task: blocks attempting to take a spa config
	    lock which won't be released until the sync task completes.
	Deadlock.

Also, since the auto trim taskq is now started asynchronously, it
may not yet be ready yet when the sync task calls spa_auto_trim().
Modified spa_auto_trim so it will simply return if the taskq is not
available yet (it will do its thing on the next pass).

Also, avoid starting auto trim taskqs for the "import$" pseudo-pool.

Also, don't attempt to create the taskq if a spa unload is in-progress.

include/sys/spa.h

@@ -796,6 +796,8 @@ extern int spa_scan_get_stats(spa_t *spa, pool_scan_stat_t *ps);
 #define	SPA_ASYNC_REMOVE_STOP			0x80
 #define	SPA_ASYNC_INITIALIZE_RESTART		0x100
 #define	SPA_ASYNC_MAN_TRIM_TASKQ_DESTROY	0x200
+#define	SPA_ASYNC_AUTO_TRIM_TASKQ_CREATE	0x400
+#define	SPA_ASYNC_AUTO_TRIM_TASKQ_DESTROY	0x800
 
 /*
  * Controls the behavior of spa_vdev_remove().

module/zfs/spa.c

@@ -3541,7 +3541,8 @@ spa_ld_get_props(spa_t *spa)
 
 		mutex_enter(&spa->spa_auto_trim_lock);
 		spa_prop_find(spa, ZPOOL_PROP_AUTOTRIM, &spa->spa_auto_trim);
-		if (spa->spa_auto_trim == SPA_AUTO_TRIM_ON)
+		if (spa->spa_auto_trim == SPA_AUTO_TRIM_ON &&
+			strcmp(spa->spa_name, TRYIMPORT_NAME) != 0)
 			spa_auto_trim_taskq_create(spa);
 		mutex_exit(&spa->spa_auto_trim_lock);
 
@@ -5306,7 +5307,8 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 
 	mutex_enter(&spa->spa_auto_trim_lock);
 	spa->spa_auto_trim = zpool_prop_default_numeric(ZPOOL_PROP_AUTOTRIM);
-	if (spa->spa_auto_trim == SPA_AUTO_TRIM_ON)
+	if (spa->spa_auto_trim == SPA_AUTO_TRIM_ON &&
+	    strcmp(spa->spa_name, TRYIMPORT_NAME) != 0)
 		spa_auto_trim_taskq_create(spa);
 	mutex_exit(&spa->spa_auto_trim_lock);
 
@@ -7250,11 +7252,27 @@ spa_async_thread(void *arg)
 		mutex_exit(&spa_namespace_lock);
 	}
 
+	/*
+	 * Trim taskq management.
+	 */
 	if (tasks & SPA_ASYNC_MAN_TRIM_TASKQ_DESTROY) {
 		mutex_enter(&spa->spa_man_trim_lock);
 		spa_man_trim_taskq_destroy(spa);
 		mutex_exit(&spa->spa_man_trim_lock);
 	}
+	if (tasks & SPA_ASYNC_AUTO_TRIM_TASKQ_CREATE) {
+		mutex_enter(&spa->spa_auto_trim_lock);
+		if (spa->spa_auto_trim_taskq == NULL)
+			spa_auto_trim_taskq_create(spa);
+		mutex_exit(&spa->spa_auto_trim_lock);
+	}
+	if (tasks & SPA_ASYNC_AUTO_TRIM_TASKQ_DESTROY) {
+		mutex_enter(&spa->spa_auto_trim_lock);
+		if (spa->spa_auto_trim_taskq != NULL)
+			spa_auto_trim_taskq_destroy(spa);
+		mutex_exit(&spa->spa_auto_trim_lock);
+	}
+
 
 	/*
 	 * Let the world know that we're done.
@@ -7768,16 +7786,9 @@ spa_sync_props(void *arg, dmu_tx_t *tx)
 				spa->spa_force_trim = intval;
 				break;
 			case ZPOOL_PROP_AUTOTRIM:
-				mutex_enter(&spa->spa_auto_trim_lock);
-				if (intval != spa->spa_auto_trim) {
-					spa->spa_auto_trim = intval;
-					if (intval != 0)
-						spa_auto_trim_taskq_create(spa);
-					else
-						spa_auto_trim_taskq_destroy(
-						    spa);
-				}
-				mutex_exit(&spa->spa_auto_trim_lock);
+				spa_async_request(spa, intval ?
+				    SPA_ASYNC_AUTO_TRIM_TASKQ_CREATE :
+				    SPA_ASYNC_AUTO_TRIM_TASKQ_DESTROY);
 				break;
 			case ZPOOL_PROP_AUTOEXPAND:
 				spa->spa_autoexpand = intval;
@@ -8509,7 +8520,6 @@ spa_auto_trim(spa_t *spa, uint64_t txg)
 {
 	ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER) == SCL_CONFIG);
 	ASSERT(!MUTEX_HELD(&spa->spa_auto_trim_lock));
-	ASSERT(spa->spa_auto_trim_taskq != NULL);
 
 	/*
 	 * Another pool management task might be currently prevented from
@@ -8519,6 +8529,12 @@ spa_auto_trim(spa_t *spa, uint64_t txg)
 	if (!mutex_tryenter(&spa->spa_auto_trim_lock))
 		return;
 
+	/* Async start-up of the auto trim taskq may not yet have completed */
+	if (spa->spa_auto_trim_taskq == NULL) {
+		mutex_exit(&spa->spa_auto_trim_lock);
+		return;
+	}
+
 	/* Count the number of auto trim threads which will be launched below */
 	/* spa->spa_num_auto_trimming += spa->spa_root_vdev->vdev_children; */
 	for (uint64_t i = 0; i < spa->spa_root_vdev->vdev_children; i++) {

module/zfs/spa_misc.c

@@ -2601,6 +2601,10 @@ spa_auto_trim_taskq_create(spa_t *spa)
 {
 	char *name = kmem_alloc(MAXPATHLEN, KM_SLEEP);
 
+	/* Don't create the taskq if the pool is unloading */
+	if (spa->spa_sync_on == B_FALSE)
+		return;
+
 	ASSERT(MUTEX_HELD(&spa->spa_auto_trim_lock));
 	ASSERT(spa->spa_auto_trim_taskq == NULL);
 	(void) snprintf(name, MAXPATHLEN, "z_atrim_%s", spa->spa_name);