On closer inspection, I'm thinking that actually it'd be a good idea if
handle_sig_alarm did what we do in, for example, HandleCatchupInterrupt:
it should save, clear, and restore ImmediateInterruptOK, so as to make
the world safe for timeout handlers to do things that might include a
CHECK_FOR_INTERRUPTS.
And while we're on the subject ... isn't bgworker_die() utterly and
completely broken? That unconditional elog(FATAL) means that no process
using that handler can do anything remotely interesting, like say touch
shared memory.
I didn't find any other similar hazards in a quick look through all our
signal handlers.
regards, tom lane
