This is passed by reference to the constructor, but a copy is saved into
the _table_shared_data member. A reference to this member is passed down
to all memtable readers. Because of the copy, the memtable readers save
a reference to the memtable_list's member, which goes away together with
the memtable_list when the storage_group is destroyed.
This causes use-after-free when a storage group is destroyed while a
memtable read is still ongoing. The memtable reader keeps the memtable
alive, but its reference to the memtable_table_shared_data becomes
stale.
Fix by saving a reference in the memtable_list too, so memtable readers
receive a reference pointing to the original replica::table member,
which is stable accross tablet migrations and merges.
The copy was introduced by 2a76065e3d.
There was a copy even before this commit, but in the previous vnode-only
world this was fine -- there was one memtable_list per table and it was
around until the table itself was. In the tablet world, this is no
longer given, but the above commit didn't account for this.
A test is included, which reproduces the use-after-free on memtable
migration. The test is somewhat artificial in that the use-after-free
would be prevented by holding on to an ERM, but this is done
intentionaly to keep the test simple. Migration -- unlike merge where
this use-after-free was originally observed -- is easy to trigger from
unit tests.
Fixes: #23762Closesscylladb/scylladb#23984
0a9ca52cfd