[PATCH 2/2] resolv: Avoid duplicate query if search list contains '.' (bug 33804)

[Florian Weimer]

* Carlos O'Donell:

> On 3/2/26 12:57 PM, Florian Weimer wrote:
>> * Carlos O'Donell:
>> 
>>>> I thought it was required because _THROW was used in NSS function
>>>> declarations (which implies attribute leaf).  But the tested functions
>>>> do not actually have this, so I can drop the volatile.  (But similar
>>>> constructs are used in other resolver tests, maybe also unnecessarily.)
>>>
>>> You are correct that __THROW implies __attribute__ ((__leaf__)) within the
>>> NSS functions, which tells the compiler they do not call back into the TUs
>>> definitions. They do call back though via response()? So you marked them
>>> volatile for that purpose? I had not considered this aspect of the
>>> implementation when I reviewed this, so I think you probably have to keep
>>> the volatile.
>>>
>>> Yes, regarding __THROW, gethostbyname, gethostbyname2, and getaddrinfo are
>>> all cancellation points and so are not marked __THROW, so they *can* call
>>> back into the caller's TU and modify data... that means volatile is not
>>> strictly required.
>>>
>>> Do we still consider these two distinct issues?
>>>
>>>   * Remove use of volatile because none of the called functions are __THROW?
>>>   * Addition of atomics to create synchronizes with behaviour to observe results?
>> Atomics are not needed because the DNS packet exchange provides
>> synchronization.  The DNS interaction completes before the getaddrinfo
>> etc. calls return to the main program.
> Within the server thread there is a call to response_callback, and during
> the execution of that function the global variable is altered along with
> the response buffer.
>
> I concur that the writev() from the server thread is sufficient to
> synchronize the contents of the buffer, but I don't see a strong guarantee
> that the global you just added has such a guarantee?

The test already fails if the query goes to a secondary server:

+  ++query_count;
   TEST_VERIFY_EXIT (qclass == C_IN);
   TEST_COMPARE (ctx->server_index, 0);

Individually, each UDP server is single-threaded.  The test does not
trigger TCP fallback, either, so we won't get parallelism from that,
either.

Thanks,
Florian