Synchronize the update of feature refcount

The concurrent execution of feature_sync() can lead to a panic due 
to an unprotected update of the feature refcount.  Resolve this by
using the spa->spa_feat_stats_lock to synchronize the update of the 
refcount.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Youzhong Yang <[email protected]>
Closes #17184
Closes #17632

Author: youzhongyang

cmd/zhack.c

@@ -363,10 +363,12 @@ feature_incr_sync(void *arg, dmu_tx_t *tx)
 	zfeature_info_t *feature = arg;
 	uint64_t refcount;
 
+	mutex_enter(&spa->spa_feat_stats_lock);
 	VERIFY0(feature_get_refcount_from_disk(spa, feature, &refcount));
 	feature_sync(spa, feature, refcount + 1, tx);
 	spa_history_log_internal(spa, "zhack feature incr", tx,
 	    "name=%s", feature->fi_guid);
+	mutex_exit(&spa->spa_feat_stats_lock);
 }
 
 static void
@@ -376,10 +378,12 @@ feature_decr_sync(void *arg, dmu_tx_t *tx)
 	zfeature_info_t *feature = arg;
 	uint64_t refcount;
 
+	mutex_enter(&spa->spa_feat_stats_lock);
 	VERIFY0(feature_get_refcount_from_disk(spa, feature, &refcount));
 	feature_sync(spa, feature, refcount - 1, tx);
 	spa_history_log_internal(spa, "zhack feature decr", tx,
 	    "name=%s", feature->fi_guid);
+	mutex_exit(&spa->spa_feat_stats_lock);
 }
 
 static void

module/zfs/zfeature.c

@@ -308,6 +308,7 @@ feature_sync(spa_t *spa, zfeature_info_t *feature, uint64_t refcount,
 	ASSERT(VALID_FEATURE_OR_NONE(feature->fi_feature));
 	uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
 	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
+	ASSERT(MUTEX_HELD(&spa->spa_feat_stats_lock));
 	VERIFY0(zap_update(spa->spa_meta_objset, zapobj, feature->fi_guid,
 	    sizeof (uint64_t), 1, &refcount, tx));
 
@@ -360,7 +361,9 @@ feature_enable_sync(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
 	    feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
 	    feature->fi_desc, tx));
 
+	mutex_enter(&spa->spa_feat_stats_lock);
 	feature_sync(spa, feature, initial_refcount, tx);
+	mutex_exit(&spa->spa_feat_stats_lock);
 
 	if (spa_feature_is_enabled(spa, SPA_FEATURE_ENABLED_TXG)) {
 		uint64_t enabling_txg = dmu_tx_get_txg(tx);
@@ -416,6 +419,7 @@ feature_do_action(spa_t *spa, spa_feature_t fid, feature_action_t action,
 	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
 
+	mutex_enter(&spa->spa_feat_stats_lock);
 	VERIFY3U(feature_get_refcount(spa, feature, &refcount), !=, ENOTSUP);
 
 	switch (action) {
@@ -433,6 +437,7 @@ feature_do_action(spa_t *spa, spa_feature_t fid, feature_action_t action,
 	}
 
 	feature_sync(spa, feature, refcount, tx);
+	mutex_exit(&spa->spa_feat_stats_lock);
 }
 
 void