Fix __zio_execute() asynchronous dispatch

To save valuable stack all zio's were made asynchronous when in the
tgx_sync_thread context or during pool initialization.  See commit
2fac4c2 for the original patch and motivation.

Unfortuantely, the changes to dsl_pool_sync_context() made by the
feature flags broke this logic causing in __zio_execute() to dispatch
itself infinitely when called during pool initialization.  This
commit refines the existing logic to specificly target only the two
cases we care about.

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 17 insertions, 9 deletions

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 66f228bc7..638105a09 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1248,7 +1248,7 @@ __zio_execute(zio_t *zio)
 	while (zio->io_stage < ZIO_STAGE_DONE) {
 		enum zio_stage pipeline = zio->io_pipeline;
 		enum zio_stage stage = zio->io_stage;
-		dsl_pool_t *dsl;
+		dsl_pool_t *dp;
 		boolean_t cut;
 		int rv;
 
@@ -1262,7 +1262,7 @@ __zio_execute(zio_t *zio)
 
 		ASSERT(stage <= ZIO_STAGE_DONE);
 
-		dsl = spa_get_dsl(zio->io_spa);
+		dp = spa_get_dsl(zio->io_spa);
 		cut = (stage == ZIO_STAGE_VDEV_IO_START) ?
 		    zio_requeue_io_start_cut_in_line : B_FALSE;
 
@@ -1272,16 +1272,24 @@ __zio_execute(zio_t *zio)
 		 * or may wait for an I/O that needs an interrupt thread
 		 * to complete, issue async to avoid deadlock.
 		 *
-		 * If we are in the txg_sync_thread or being called
-		 * during pool init issue async to minimize stack depth.
-		 * Both of these call paths may be recursively called.
-		 *
 		 * For VDEV_IO_START, we cut in line so that the io will
 		 * be sent to disk promptly.
 		 */
-		if (((stage & ZIO_BLOCKING_STAGES) && zio->io_vd == NULL &&
-		    zio_taskq_member(zio, ZIO_TASKQ_INTERRUPT)) ||
-		    (dsl != NULL && dsl_pool_sync_context(dsl))) {
+		if ((stage & ZIO_BLOCKING_STAGES) && zio->io_vd == NULL &&
+		    zio_taskq_member(zio, ZIO_TASKQ_INTERRUPT)) {
+			zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE, cut);
+			return;
+		}
+
+		/*
+		 * If we executing in the context of the tx_sync_thread,
+		 * or we are performing pool initialization outside of a
+		 * zio_taskq[ZIO_TASKQ_ISSUE] context.  Then issue the zio
+		 * async to minimize stack usage for these deep call paths.
+		 */
+		if ((dp && curthread == dp->dp_tx.tx_sync_thread) ||
+		    (dp && spa_is_initializing(dp->dp_spa) &&
+		    !zio_taskq_member(zio, ZIO_TASKQ_ISSUE))) {
 			zio_taskq_dispatch(zio, ZIO_TASKQ_ISSUE, cut);
 			return;
 		}