Re: [HACKERS] possible self-deadlock window after bad ProcessStartupPacket

On Thu, Jun 22, 2017 at 03:10:31PM -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > Or, probably more robust: Simply _exit(2) without further ado, and rely
> > on postmaster to output an appropriate error message. Arguably it's not
> > actually useful to see hundreds of "WARNING: terminating connection because of
> > crash of another server process" messages in the log anyway.
>
> At that point you might as well skip the entire mechanism and go straight
> to SIGKILL. IMO the only reason quickdie() exists at all is to try to
> send a helpful message to the client. And it is helpful --- your attempt
> to claim that it isn't sounds very much like wishful thinking.

I dunno if it is or isn't helpful. But I do know that this must be done
in an async-signal-safe way.

Besides making ereport() async-signal-safe, which is tricky, you could
write(2) the arguments to a pipe that another thread in the same process
is reading from and which will then call ereport() and exit(3). This
would be less work if you're willing to use a thread for that (the
thread would only block in read(2) on that pipe, and would only provide
this one service).

Nico
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