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-rw-r--r--module/zfs/metaslab.c25
1 files changed, 22 insertions, 3 deletions
diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c
index 46543a52b..6d6ff0914 100644
--- a/module/zfs/metaslab.c
+++ b/module/zfs/metaslab.c
@@ -1242,6 +1242,8 @@ metaslab_preload(void *arg)
metaslab_t *msp = arg;
spa_t *spa = msp->ms_group->mg_vd->vdev_spa;
+ ASSERT(!MUTEX_HELD(&msp->ms_group->mg_lock));
+
mutex_enter(&msp->ms_lock);
metaslab_load_wait(msp);
if (!msp->ms_loaded)
@@ -1266,19 +1268,36 @@ metaslab_group_preload(metaslab_group_t *mg)
taskq_wait(mg->mg_taskq);
return;
}
- mutex_enter(&mg->mg_lock);
+ mutex_enter(&mg->mg_lock);
/*
- * Prefetch the next potential metaslabs
+ * Load the next potential metaslabs
*/
- for (msp = avl_first(t); msp != NULL; msp = AVL_NEXT(t, msp)) {
+ msp = avl_first(t);
+ while (msp != NULL) {
+ metaslab_t *msp_next = AVL_NEXT(t, msp);
/* If we have reached our preload limit then we're done */
if (++m > metaslab_preload_limit)
break;
+ /*
+ * We must drop the metaslab group lock here to preserve
+ * lock ordering with the ms_lock (when grabbing both
+ * the mg_lock and the ms_lock, the ms_lock must be taken
+ * first). As a result, it is possible that the ordering
+ * of the metaslabs within the avl tree may change before
+ * we reacquire the lock. The metaslab cannot be removed from
+ * the tree while we're in syncing context so it is safe to
+ * drop the mg_lock here. If the metaslabs are reordered
+ * nothing will break -- we just may end up loading a
+ * less than optimal one.
+ */
+ mutex_exit(&mg->mg_lock);
VERIFY(taskq_dispatch(mg->mg_taskq, metaslab_preload,
msp, TQ_PUSHPAGE) != 0);
+ mutex_enter(&mg->mg_lock);
+ msp = msp_next;
}
mutex_exit(&mg->mg_lock);
}