Re: [RFC][PATCH v2 1/2][PR gdb/24069] [delete] Not-so-harmless spurious call to `wait4`

[Philippe Blain via Gdb-patches <gdb-patches@sourceware.org>]

Hi Simon,

Le 2022-02-19 à 10:47, Simon Marchi a écrit :
> On 2022-02-16 09:15, Philippe Blain wrote:
>> From: Dominique Quatravaux <dominique.quatravaux@epfl.ch>
>>
>> As seen in https://sourceware.org/bugzilla/show_bug.cgi?id=24069 this
>> code will typically wait4() a second time on the same process that was
>> already wait4()'d a few lines above. While this used to be
>> harmless/idempotent (when we assumed that the process already exited),
>> this now causes a deadlock in the WIFSTOPPED case.
>>
>> The early (~2019) history of bug #24069 cautiously suggests to use
>> WNOHANG instead of outright deleting the call. However, tests on the
>> current version of Darwin (Big Sur) demonstrate that gdb runs just
>> fine without a redundant call to wait4(), as would be expected.
>> Notwithstanding the debatable value of conserving bug compatibility
>> with an OS release that is more than a decade old, there is scant
>> evidence of what that double-wait4() was supposed to achieve in the
>> first place - A cursory investigation with `git blame` pinpoints
>> commits bb00b29d7802 and a80b95ba67e2 from the 2008-2009 era, but
>> fails to answer the “why” question conclusively.
> 
> Given that this additional wait does not seem logical at all and
> empirical evidence shows that it's not right, I'm fine with merging
> this one directly.  Do you have push access, or would you like me to do
> it on your behalf?
> 
> Simon
> 

I do not have push access, so yes, if you think that it's a good idea to merge
this one directly, please go ahead. I think it won't solve all problems on its
own, but the bugzilla history indicates it would at least be a good start.

I did include a changelog entry, so that it could also be included in an eventual 
11.3 release if you think it makes sense.

Thanks!

Philippe.