Hi Ilya,

The patch LGTM, thanks.

          Alexander 
>Вторник, 15 октября 2019, 18:50 +03:00 от Ilya Kosarev <i.kosarev@tarantool.org>:
>
>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 |  2 ++
> 2 files changed, 26 insertions(+), 1 deletion(-)
>
>diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
>index eb11346c1..325129a6e 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);
>@@ -528,6 +533,18 @@ 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..43e16879d 100644
>--- a/src/box/memtx_engine.h
>+++ b/src/box/memtx_engine.h
>@@ -107,6 +107,8 @@ 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 **/
>+	struct cord *replica_join_cord;
> 	/** Common quota for tuples and indexes. */
> 	struct quota quota;
> 	/**
>-- 
>2.17.1
>
>


-- 
Alexander Tikhonov