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

[Florian Weimer <fweimer@redhat.com>]

* 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.

Thanks,
Florian