From 54a179e7b80413bd48cd2cd259110fb493d0215e Mon Sep 17 00:00:00 2001
From: "Ricardo M. Correia" <ricardo.correia@oracle.com>
Date: Fri, 21 Jan 2011 14:35:41 -0800
Subject: Add API to wait for pending commit callbacks

This adds an API to wait for pending commit callbacks of already-synced
transactions to finish processing.  This is needed by the DMU-OSD in
Lustre during device finalization when some callbacks may still not be
called, this leads to non-zero reference count errors.  See lustre.org
bug 23931.
---
 include/sys/txg.h       |  6 ++++++
 module/zfs/dmu_objset.c |  1 +
 module/zfs/txg.c        | 15 +++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/include/sys/txg.h b/include/sys/txg.h
index e323d5efabb7..263693846d54 100644
--- a/include/sys/txg.h
+++ b/include/sys/txg.h
@@ -107,6 +107,12 @@ extern boolean_t txg_stalled(struct dsl_pool *dp);
 /* returns TRUE if someone is waiting for the next txg to sync */
 extern boolean_t txg_sync_waiting(struct dsl_pool *dp);
 
+/*
+ * Wait for pending commit callbacks of already-synced transactions to finish
+ * processing.
+ */
+extern void txg_wait_callbacks(struct dsl_pool *dp);
+
 /*
  * Per-txg object lists.
  */
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c
index 7da5c1aa08f5..0ff95a64e0bd 100644
--- a/module/zfs/dmu_objset.c
+++ b/module/zfs/dmu_objset.c
@@ -1813,6 +1813,7 @@ EXPORT_SYMBOL(dmu_objset_destroy);
 EXPORT_SYMBOL(dmu_objset_snapshot);
 EXPORT_SYMBOL(dmu_objset_stats);
 EXPORT_SYMBOL(dmu_objset_fast_stat);
+EXPORT_SYMBOL(dmu_objset_spa);
 EXPORT_SYMBOL(dmu_objset_space);
 EXPORT_SYMBOL(dmu_objset_fsid_guid);
 EXPORT_SYMBOL(dmu_objset_find);
diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index 382a2a91c7b0..5afb139ddfb0 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -350,6 +350,20 @@ txg_dispatch_callbacks(dsl_pool_t *dp, uint64_t txg)
 	}
 }
 
+/*
+ * Wait for pending commit callbacks of already-synced transactions to finish
+ * processing.
+ * Calling this function from within a commit callback will deadlock.
+ */
+void
+txg_wait_callbacks(dsl_pool_t *dp)
+{
+	tx_state_t *tx = &dp->dp_tx;
+
+	if (tx->tx_commit_cb_taskq != NULL)
+		taskq_wait(tx->tx_commit_cb_taskq);
+}
+
 static void
 txg_sync_thread(dsl_pool_t *dp)
 {
@@ -735,6 +749,7 @@ EXPORT_SYMBOL(txg_register_callbacks);
 EXPORT_SYMBOL(txg_delay);
 EXPORT_SYMBOL(txg_wait_synced);
 EXPORT_SYMBOL(txg_wait_open);
+EXPORT_SYMBOL(txg_wait_callbacks);
 EXPORT_SYMBOL(txg_stalled);
 EXPORT_SYMBOL(txg_sync_waiting);
 #endif
-- 
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