Fix a race condition in dsl_dataset_sync() when activating features

The zio returned from arc_write() in dmu_objset_sync() uses
zio_nowait(). However we may reach the end of dsl_dataset_sync()
which checks if we need to activate features in the filesystem
without knowing if that zio has even run through the ZIO pipeline yet.
In that case we will flag features to be activated in
dsl_dataset_block_born() but dsl_dataset_sync() has already
completed its run and those features will not actually be activated.
Mitigate this by moving the feature activation code in
dsl_dataset_sync_done(). Also add new ASSERTs in
dsl_scan_visitbp() checking if a block contradicts any filesystem
flags.

Reviewed-by: Matthew Ahrens <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Brian Atkinson <[email protected]>
Signed-off-by: George Amanakis <[email protected]>
Closes #13816 

3 files changed, 33 insertions, 11 deletions

diff --git a/module/zfs/dmu_send.c b/module/zfs/dmu_send.c
index 7f8de23f0..33beb04b1 100644
--- a/module/zfs/dmu_send.c
+++ b/module/zfs/dmu_send.c
@@ -493,6 +493,7 @@ dmu_dump_write(dmu_send_cookie_t *dscp, dmu_object_type_t type, uint64_t object,
 	    (bp != NULL ? BP_GET_COMPRESS(bp) != ZIO_COMPRESS_OFF &&
 	    io_compressed : lsize != psize);
 	if (raw || compressed) {
+		ASSERT(bp != NULL);
 		ASSERT(raw || dscp->dsc_featureflags &
 		    DMU_BACKUP_FEATURE_COMPRESSED);
 		ASSERT(!BP_IS_EMBEDDED(bp));
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 57a58f88c..0584a356f 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -1039,7 +1039,7 @@ dsl_dataset_has_owner(dsl_dataset_t *ds)
 	return (rv);
 }
 
-static boolean_t
+boolean_t
 zfeature_active(spa_feature_t f, void *arg)
 {
 	switch (spa_feature_table[f].fi_type) {
@@ -2121,16 +2121,6 @@ dsl_dataset_sync(dsl_dataset_t *ds, zio_t *zio, dmu_tx_t *tx)
 	}
 
 	dmu_objset_sync(ds->ds_objset, zio, tx);
-
-	for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
-		if (zfeature_active(f, ds->ds_feature_activation[f])) {
-			if (zfeature_active(f, ds->ds_feature[f]))
-				continue;
-			dsl_dataset_activate_feature(ds->ds_object, f,
-			    ds->ds_feature_activation[f], tx);
-			ds->ds_feature[f] = ds->ds_feature_activation[f];
-		}
-	}
 }
 
 /*
@@ -2303,6 +2293,17 @@ dsl_dataset_sync_done(dsl_dataset_t *ds, dmu_tx_t *tx)
 	ASSERT(!dmu_objset_is_dirty(os, dmu_tx_get_txg(tx)));
 
 	dmu_buf_rele(ds->ds_dbuf, ds);
+
+	for (spa_feature_t f = 0; f < SPA_FEATURES; f++) {
+		if (zfeature_active(f,
+		    ds->ds_feature_activation[f])) {
+			if (zfeature_active(f, ds->ds_feature[f]))
+				continue;
+			dsl_dataset_activate_feature(ds->ds_object, f,
+			    ds->ds_feature_activation[f], tx);
+			ds->ds_feature[f] = ds->ds_feature_activation[f];
+		}
+	}
 }
 
 int
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index 2cc77eab6..f971aa211 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -2038,6 +2038,26 @@ dsl_scan_visitbp(blkptr_t *bp, const zbookmark_phys_t *zb,
 		return;
 	}
 
+	/*
+	 * Check if this block contradicts any filesystem flags.
+	 */
+	spa_feature_t f = SPA_FEATURE_LARGE_BLOCKS;
+	if (BP_GET_LSIZE(bp) > SPA_OLD_MAXBLOCKSIZE)
+		ASSERT(dsl_dataset_feature_is_active(ds, f));
+
+	f = zio_checksum_to_feature(BP_GET_CHECKSUM(bp));
+	if (f != SPA_FEATURE_NONE)
+		ASSERT(dsl_dataset_feature_is_active(ds, f));
+
+	f = zio_compress_to_feature(BP_GET_COMPRESS(bp));
+	if (f != SPA_FEATURE_NONE)
+		ASSERT(dsl_dataset_feature_is_active(ds, f));
+
+	if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg) {
+		scn->scn_lt_min_this_txg++;
+		return;
+	}
+
 	if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg) {
 		scn->scn_lt_min_this_txg++;
 		return;