try long hold approach

include/sys/dsl_dir.h

@@ -120,8 +120,10 @@ struct dsl_dir {
 	dsl_deadlist_t dd_livelist;
 	bplist_t dd_pending_frees;
 	bplist_t dd_pending_allocs;
+
 	kmutex_t dd_activity_lock;
 	kcondvar_t dd_activity_cv;
+	boolean_t dd_activity_cancelled;
 
 	/* protected by dd_lock; keep at end of struct for better locality */
 	char dd_myname[ZFS_MAX_DATASET_NAME_LEN];
@@ -194,7 +196,7 @@ boolean_t dsl_dir_is_zapified(dsl_dir_t *dd);
 void dsl_dir_livelist_open(dsl_dir_t *dd, uint64_t obj);
 void dsl_dir_livelist_close(dsl_dir_t *dd);
 void dsl_dir_remove_livelist(dsl_dir_t *dd, dmu_tx_t *tx, boolean_t total);
-int dsl_dir_wait(dsl_dir_t *dd, zfs_wait_activity_t activity,
+int dsl_dir_wait(dsl_dir_t *dd, dsl_dataset_t *ds, zfs_wait_activity_t activity,
     boolean_t *waited);
 
 /* internal reserved dir name */

module/os/linux/zfs/zfs_vfsops.c

@@ -54,6 +54,7 @@
 #include <sys/zfs_fuid.h>
 #include <sys/sunddi.h>
 #include <sys/dmu_objset.h>
+#include <sys/dsl_dir.h>
 #include <sys/spa_boot.h>
 #include <sys/objlist.h>
 #include <sys/zpl.h>
@@ -1319,6 +1320,8 @@ zfsvfs_setup(zfsvfs_t *zfsvfs, boolean_t mounting)
 			    "num_entries in unlinked set: %llu",
 			    zs.zs_num_entries);
 			zfs_unlinked_drain(zfsvfs);
+			dsl_dir_t *dd = zfsvfs->z_os->os_dsl_dataset->ds_dir;
+			dd->dd_activity_cancelled = B_FALSE;
 		}
 
 		/*
@@ -1869,6 +1872,9 @@ zfsvfs_teardown(zfsvfs_t *zfsvfs, boolean_t unmounting)
 		txg_wait_synced(dmu_objset_pool(zfsvfs->z_os), 0);
 	}
 	dmu_objset_evict_dbufs(zfsvfs->z_os);
+	dsl_dir_t *dd = os->os_dsl_dataset->ds_dir;
+	dd->dd_activity_cancelled = B_TRUE;
+	cv_broadcast(&dd->dd_activity_cv);
 
 	return (0);
 }
@@ -2256,6 +2262,7 @@ zfs_resume_fs(zfsvfs_t *zfsvfs, dsl_dataset_t *ds)
 	if (err != 0)
 		goto bail;
 
+	ds->ds_dir->dd_activity_cancelled = B_FALSE;
 	VERIFY(zfsvfs_setup(zfsvfs, B_FALSE) == 0);
 
 	zfs_set_fuid_feature(zfsvfs);

module/zfs/dsl_dir.c

@@ -160,6 +160,8 @@ dsl_dir_evict_async(void *dbu)
 		dsl_dir_livelist_close(dd);
 
 	dsl_prop_fini(dd);
+	cv_destroy(&dd->dd_activity_cv);
+	mutex_destroy(&dd->dd_activity_lock);
 	mutex_destroy(&dd->dd_lock);
 	kmem_free(dd, sizeof (dsl_dir_t));
 }
@@ -314,6 +316,8 @@ dsl_dir_hold_obj(dsl_pool_t *dp, uint64_t ddobj,
 	if (dsl_deadlist_is_open(&dd->dd_livelist))
 		dsl_dir_livelist_close(dd);
 	dsl_prop_fini(dd);
+	cv_destroy(&dd->dd_activity_cv);
+	mutex_destroy(&dd->dd_activity_lock);
 	mutex_destroy(&dd->dd_lock);
 	kmem_free(dd, sizeof (dsl_dir_t));
 	dmu_buf_rele(dbuf, tag);
@@ -2285,41 +2289,31 @@ dsl_dir_remove_livelist(dsl_dir_t *dd, dmu_tx_t *tx, boolean_t total)
 }
 
 static int
-dsl_dir_activity_in_progress(dsl_dir_t *dd, zfs_wait_activity_t activity,
-    boolean_t *in_progress)
+dsl_dir_activity_in_progress(dsl_dir_t *dd, dsl_dataset_t *ds,
+    zfs_wait_activity_t activity, boolean_t *in_progress)
 {
 	int error = 0;
-	zfs_dbgmsg("progress %px %d", dd, activity);
 
 	ASSERT(MUTEX_HELD(&dd->dd_activity_lock));
 
 	switch (activity) {
 	case ZFS_WAIT_DELETEQ: {
-		dsl_dataset_t *ds;
-		error = dsl_dataset_hold_obj(dd->dd_pool,
-		    dsl_dir_phys(dd)->dd_head_dataset_obj, FTAG, &ds);
-		if (error != 0)
-			break;
 		objset_t *os;
 		error = dmu_objset_from_ds(ds, &os);
 		if (error != 0)
 			break;
 
 		uint64_t count, unlinked_obj;
-		zfs_dbgmsg("os %px", os);
 		error = zap_lookup(os, MASTER_NODE_OBJ, ZFS_UNLINKED_SET, 8, 1,
 		    &unlinked_obj);
 		if (error != 0) {
 			dsl_dataset_rele(ds, FTAG);
 			break;
 		}
-		zfs_dbgmsg("obj %ld", unlinked_obj);
 		error = zap_count(os, unlinked_obj, &count);
 
 		if (error == 0)
 			*in_progress = (count != 0);
-
-		dsl_dataset_rele(ds, FTAG);
 		break;
 	}
 	default:
@@ -2330,22 +2324,22 @@ dsl_dir_activity_in_progress(dsl_dir_t *dd, zfs_wait_activity_t activity,
 }
 
 int
-dsl_dir_wait(dsl_dir_t *dd, zfs_wait_activity_t activity, boolean_t *waited)
+dsl_dir_wait(dsl_dir_t *dd, dsl_dataset_t *ds, zfs_wait_activity_t activity,
+    boolean_t *waited)
 {
 	int error = 0;
 	boolean_t in_progress;
-	zfs_dbgmsg("waiting %px %d", dd, activity);
 	mutex_enter(&dd->dd_activity_lock);
 	for (;;) {
-		error = dsl_dir_activity_in_progress(dd, activity,
+		error = dsl_dir_activity_in_progress(dd, ds, activity,
 		    &in_progress);
 		if (error != 0 || !in_progress)
 			break;
 
 		*waited = B_TRUE;
 
 		if (cv_wait_sig(&dd->dd_activity_cv, &dd->dd_activity_lock) ==
-		    0) {
+		    0 || dd->dd_activity_cancelled) {
 			error = EINTR;
 			break;
 		}

module/zfs/zfs_ioctl.c

@@ -4114,6 +4114,7 @@ zfs_ioc_wait_fs(const char *name, nvlist_t *innvl, nvlist_t *outnvl)
 	int error;
 	dsl_pool_t *dp;
 	dsl_dir_t *dd;
+	dsl_dataset_t *ds;
 
 	if (nvlist_lookup_int32(innvl, ZFS_WAIT_ACTIVITY, &activity) != 0)
 		return (EINVAL);
@@ -4125,10 +4126,21 @@ zfs_ioc_wait_fs(const char *name, nvlist_t *innvl, nvlist_t *outnvl)
 		return (error);
 	}
 
-	error = dsl_dir_wait(dd, activity, &waited);
-	dsl_dir_rele(dd, FTAG);
+	if ((error = dsl_dataset_hold_obj(dd->dd_pool,
+	    dsl_dir_phys(dd)->dd_head_dataset_obj, FTAG, &ds)) != 0) {
+		dsl_pool_rele(dp, FTAG);
+		dsl_dir_rele(dd, FTAG);
+		return (error);
+	}
+	dsl_dataset_long_hold(ds, FTAG);
 	dsl_pool_rele(dp, FTAG);
 
+	error = dsl_dir_wait(dd, ds, activity, &waited);
+
+	dsl_dataset_long_rele(ds, FTAG);
+	dsl_dataset_rele(ds, FTAG);
+	dsl_dir_rele(dd, FTAG);
+
 	if (error == 0)
 		fnvlist_add_boolean_value(outnvl, ZFS_WAIT_WAITED, waited);