The `system_table_corrupt_data_handler::_fragment_semaphore` member is
initialized only when the `system_keyspace` sharded service is
initialized by `main`. If the server shuts down before that due to an
unrelated reason, `_fragment_semaphore` remains default-initialized to
`nullptr`. When the shutdown process later attempts to call `stop()` on
`system_table_corrupt_data_handler`, it tries to call `stop()` on
`_fragment_semaphore`, leading to a segfault.
Fix this by checking if `_fragment_semaphore` is null before invoking
`stop()` on it.
Although `corrupt_data_handler` was backported to 2025.1, this issue
does not occur in 2025.2 and master. The recent versions include #23113,
which changes how the system keyspace is stopped and PR #24492, which
originally introduced `corrupt_data_handler`, builds on that change to
ensure `_fragment_semaphore` is stopped only if it has been created.
Fixes#24920
Signed-off-by: Lakshmi Narayanan Sreethar <lakshmi.sreethar@scylladb.com>
Closesscylladb/scylladb#24931
Similar to large_data_handler, this interface allows sstable writers to
delegate the handling of corrupt data.
Two implementations are provided:
* system_table_corrupt_data_handler - saved corrupt data in
system.corrupt_data, with a TTL=10days (non-configurable for now)
* nop_corrupt_data_handler - drops corrupt data
(cherry picked from commit 3e1c50e9a7)
