[Tarantool-patches] [PATCH] replication: cancel replica joining thread at exit

[Ilya Kosarev]

If a tarantool instance exits while joining replica is in progress,
the replica joining thread can access already freed data resulting
in a crash. Let's fix this the same way we did for checkpoint thread
- simply cancel the thread forcefully and wait for it to terminate.

Closes #4528
---
https://github.com/tarantool/tarantool/tree/i.kosarev/gh-4528-fix-shutdown-on-replica-join
https://github.com/tarantool/tarantool/issues/4528

 src/box/memtx_engine.c | 25 ++++++++++++++++++++++++-
 src/box/memtx_engine.h |  5 +++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
index ecce3b1b6..23ccc4703 100644
--- a/src/box/memtx_engine.c
+++ b/src/box/memtx_engine.c
@@ -55,6 +55,9 @@
 static void
 checkpoint_cancel(struct checkpoint *ckpt);
 
+static void
+replica_join_cancel(struct cord *replica_join_cord);
+
 struct PACKED memtx_tuple {
 	/*
 	 * sic: the header of the tuple is used
@@ -129,6 +132,8 @@ memtx_engine_shutdown(struct engine *engine)
 	struct memtx_engine *memtx = (struct memtx_engine *)engine;
 	if (memtx->checkpoint != NULL)
 		checkpoint_cancel(memtx->checkpoint);
+	if (memtx->replica_join_cord != NULL)
+		replica_join_cancel(memtx->replica_join_cord);
 	mempool_destroy(&memtx->iterator_pool);
 	if (mempool_is_initialized(&memtx->rtree_iterator_pool))
 		mempool_destroy(&memtx->rtree_iterator_pool);
@@ -527,6 +532,18 @@ checkpoint_cancel(struct checkpoint *ckpt)
 	checkpoint_delete(ckpt);
 }
 
+static void
+replica_join_cancel(struct cord *replica_join_cord)
+{
+	/*
+	 * Cancel the thread being used to join replica if it's
+	 * running and wait for it to terminate so as to
+	 * eliminate the possibility of use-after-free.
+	 */
+	tt_pthread_cancel(replica_join_cord->id);
+	tt_pthread_join(replica_join_cord->id, NULL);
+}
+
 static int
 checkpoint_add_space(struct space *sp, void *data)
 {
@@ -848,7 +865,11 @@ memtx_engine_join(struct engine *engine, void *arg, struct xstream *stream)
 	struct cord cord;
 	if (cord_costart(&cord, "initial_join", memtx_join_f, ctx) != 0)
 		return -1;
-	return cord_cojoin(&cord);
+	struct memtx_engine *memtx = (struct memtx_engine *)engine;
+	memtx->replica_join_cord = &cord;
+	int res = cord_cojoin(&cord);
+	memtx->replica_join_cord = NULL;
+	return res;
 }
 
 static void
@@ -1030,6 +1051,8 @@ memtx_engine_new(const char *snap_dirname, bool force_recovery,
 	memtx->max_tuple_size = MAX_TUPLE_SIZE;
 	memtx->force_recovery = force_recovery;
 
+	memtx->replica_join_cord = NULL;
+
 	memtx->base.vtab = &memtx_engine_vtab;
 	memtx->base.name = "memtx";
 
diff --git a/src/box/memtx_engine.h b/src/box/memtx_engine.h
index c092f5d8e..f562c66df 100644
--- a/src/box/memtx_engine.h
+++ b/src/box/memtx_engine.h
@@ -107,6 +107,11 @@ struct memtx_engine {
 	uint64_t snap_io_rate_limit;
 	/** Skip invalid snapshot records if this flag is set. */
 	bool force_recovery;
+	/**
+	 * Cord being currently used to join replica. It is only
+	 * needed to be able to cancel it on shutdown.
+	 */
+	struct cord *replica_join_cord;
 	/** Common quota for tuples and indexes. */
 	struct quota quota;
 	/**
-- 
2.17.1