MFV r249857:

Merge vendor bugfix for a possible deadlock related to async destroy
and improve write performance by introducing a new lock protecting
tx_open_txg.

Illumos ZFS issues:
  3642 dsl_scan_active() should not issue I/O to determine if async
       destroying is active
  3643 txg_delay should not hold the tc_lock

MFC after:	1 week

1 files changed, 12 insertions, 6 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
index 7be37db..46b5c34 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
@@ -132,6 +132,8 @@ txg_init(dsl_pool_t *dp, uint64_t txg)
 		int i;
 
 		mutex_init(&tx->tx_cpu[c].tc_lock, NULL, MUTEX_DEFAULT, NULL);
+		mutex_init(&tx->tx_cpu[c].tc_open_lock, NULL, MUTEX_DEFAULT,
+		    NULL);
 		for (i = 0; i < TXG_SIZE; i++) {
 			cv_init(&tx->tx_cpu[c].tc_cv[i], NULL, CV_DEFAULT,
 			    NULL);
@@ -174,6 +176,7 @@ txg_fini(dsl_pool_t *dp)
 	for (c = 0; c < max_ncpus; c++) {
 		int i;
 
+		mutex_destroy(&tx->tx_cpu[c].tc_open_lock);
 		mutex_destroy(&tx->tx_cpu[c].tc_lock);
 		for (i = 0; i < TXG_SIZE; i++) {
 			cv_destroy(&tx->tx_cpu[c].tc_cv[i]);
@@ -297,10 +300,12 @@ txg_hold_open(dsl_pool_t *dp, txg_handle_t *th)
 	tx_cpu_t *tc = &tx->tx_cpu[CPU_SEQID];
 	uint64_t txg;
 
-	mutex_enter(&tc->tc_lock);
-
+	mutex_enter(&tc->tc_open_lock);
 	txg = tx->tx_open_txg;
+
+	mutex_enter(&tc->tc_lock);
 	tc->tc_count[txg & TXG_MASK]++;
+	mutex_exit(&tc->tc_lock);
 
 	th->th_cpu = tc;
 	th->th_txg = txg;
@@ -313,7 +318,8 @@ txg_rele_to_quiesce(txg_handle_t *th)
 {
 	tx_cpu_t *tc = th->th_cpu;
 
-	mutex_exit(&tc->tc_lock);
+	ASSERT(!MUTEX_HELD(&tc->tc_lock));
+	mutex_exit(&tc->tc_open_lock);
 }
 
 void
@@ -350,10 +356,10 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg)
 	int c;
 
 	/*
-	 * Grab all tx_cpu locks so nobody else can get into this txg.
+	 * Grab all tc_open_locks so nobody else can get into this txg.
 	 */
 	for (c = 0; c < max_ncpus; c++)
-		mutex_enter(&tx->tx_cpu[c].tc_lock);
+		mutex_enter(&tx->tx_cpu[c].tc_open_lock);
 
 	ASSERT(txg == tx->tx_open_txg);
 	tx->tx_open_txg++;
@@ -363,7 +369,7 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg)
 	 * enter the next transaction group.
 	 */
 	for (c = 0; c < max_ncpus; c++)
-		mutex_exit(&tx->tx_cpu[c].tc_lock);
+		mutex_exit(&tx->tx_cpu[c].tc_open_lock);
 
 	/*
 	 * Quiesce the transaction group by waiting for everyone to txg_exit().