We currently have races, like between moving an sstable from staging
using change_state, or when taking a snapshot, to e.g.
rewrite_statistics that replaces one of the sstable component files
when called, for example, from update_repaired_at by incremental repair.
Use a semaphore as a mutex to serialize those functions.
Note that there is no need for rwlock since the operations
are rare and read-only operations like snapshot don't
need to run in parallel.
Fixes#25919
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
9e18cfbe17