Re: [PATCH] __check_pf: Add a cancellation cleanup handler [BZ #20975]

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Apr 28, 2023 at 1:38 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > There are reports for hang in __check_pf:
> >
> > https://github.com/JoeDog/siege/issues/4
> >
> > It is reproducible only under specific configurations:
> >
> > 1. Large number of cores (>= 64) and large number of threads (> 3X of
> > the number of cores) with long lived socket connection.
> > 2. Low power (frequency) mode.
> > 3. Power management is enabled.
> >
> > While holding lock, __check_pf calls make_request which calls __sendto
> > and __recvmsg.  Since __sendto and __recvmsg are cancellation points,
> > lock held by __check_pf won't be released and can cause deadlock when
> > thread cancellation happens in __sendto or __recvmsg.  Add a cancellation
> > cleanup handler for __check_pf to unlock the lock when cancelled by
> > another thread.  This fixes BZ #20975 and the siege hang issue.
>
> It's probably easier to reproduce if the system has many network
> interfaces with lots of addresses.
>
> Doesn't getaddrinfo leak all kind of resources when canceled?  That's
> more difficult to fix, though.

We will work on it if there are reports.

-- 
H.J.