Subject: Re: [PATCH 3/4] http.c: avoid danging pointer to local variable `finished`

From: Junio C Hamano <[email-masked]>
Date: Tue, 24 May 2022 13:06:02 -0700

Ævar Arnfjörð Bjarmason <[email-masked]> writes:

> On Tue, May 24 2022, Johannes Schindelin via GitGitGadget wrote:
>
>> From: Johannes Schindelin <[email-masked]>
>> [...]
>> Let's drop that local variable and introduce a new flag in the slot that
>> is used to indicate that even while the slot is no longer in use, it is
>> still reserved until further notice. It is the responsibility of
>> `run_active_slot()` to clear that flag once it is done with that slot.
>>
>> Initial-patch-by: Junio C Hamano <[email-masked]>
>
> Don't you mean by me?
> I.e. https://lore.kernel.org/git/[email-masked]/

Most likely, but this version is so distant from the "clear
slot->finished before leaving run_active_slot()" Dscho and I were
recently discussing, that I do not think it can be said to have been
derived from that one.  This is completely a different patch that
makes different changes.

The "clear slot->finished", by the way, is what I think is the right
thing to do, especially that the objective is to squelch the false
positive warning from a new compiler.  If there is a way to annotate
the line for the compiler to tell it not to warn about it, that would
have been even better.

> This seems to be derived from that, or perhaps you just came up with
> something similar independently. Junio then came up with the smaller
> https://lore.kernel.org/git/[email-masked]/

I actually do not think so.  Yours is revert of the existing fix the
compiler is confused about, and I have a feeling that if the original
fix is still relevant, the problem the original fix wanted to address
will resurface as a regression.

If I am reading the patch correctly, Dscho's is to avoid [*] reusing
a slot while any run_active_slot() is still waiting for its
completion.  The approach would solve the problem the original fix
wanted to solve in a different way.  Personally I do not think such
a surgery is necessary only to squelch false positives from a new
warning compiler, though.

[Footnote] 

 * I said "is to avoid", not "avoids", because I haven't studied the
   patch with sufficient degree of carefulness to say for sure, even
   though I can see that is the intent.