When a user backend (as opposed to vacuum or autoanalyze) gets burdened with cleaning up the GIN pending list, it does not call CHECK_FOR_INTERRUPTS().
Since cleaning does a lot of random IO, it can take a long time and it is not nice to be uninterruptable.
The attached patch adds an else branch to call CHECK_FOR_INTERRUPTS().
But I think we could instead just call vacuum_delay_point unconditionally. It calls CHECK_FOR_INTERRUPTS(), and if not in a throttled vacuum it does nothing else. (That is how ANALYZE handles it.)
This issue is in all branches.
Cheers,
Jeff