# Re: \[PATCH v12 22/22\] selftests/vm: Fix deadlock in protection\_keys.c

- From: Dave Hansen \<hidden\>
- Date: 2018-03-16 22:35:02 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2018/03/5218931
- Thread: https://ratatoskr.run/linux-kselftest/2018/02/5195852/t.md

```text
On 02/21/2018 05:55 PM, Ram Pai wrote:
> From: Thiago Jung Bauermann <redacted>
> 
> The sig_chld() handler calls dprintf2() taking care of setting
> dprint_in_signal so that sigsafe_printf() won't call printf().
> Unfortunately, this precaution is is negated by dprintf_level(), which
> has a call to fflush().
> 
> This function acquires a lock, which means that if the signal interrupts an
> ongoing fflush() the process will deadlock. At least on powerpc this is
> easy to trigger, resulting in the following backtrace when attaching to the
> frozen process:

Ugh, yeah, I've run into this too.

Acked-by: Dave Hansen <redacted>
```