Re: bug in futex.2, FUTEX_CMP_REQUEUE

[Carlos O'Donell <carlos@redhat.com>]

On 5/27/25 8:51 AM, Alejandro Colomar wrote:
> Hi Carlos,
> 
> On Tue, May 27, 2025 at 08:37:16AM -0400, Carlos O'Donell wrote:
>> Since the parenthetical is not clear about val vs. val2, it can be
>> read in two different ways.
> 
> The entire paragraph is
> 
>              Typical  values to specify for val are 0 or 1.  (Specifying
>              INT_MAX is not  useful,  because  it  would  make  the  FU‐
>              TEX_CMP_REQUEUE  operation  equivalent to FUTEX_WAKE.)  The
>              limit value specified via val2 is  typically  either  1  or
>              INT_MAX.   (Specifying the argument as 0 is not useful, be‐
>              cause it would make the FUTEX_CMP_REQUEUE operation equiva‐
>              lent to FUTEX_WAIT.)
> 
> 
> There's a parenthetical after talking about val, and another one after
> talking about val2.  I think the latter parenthetical unambiguously
> refers to val2.  I would have written them as part of each sentence, to
> make it even less ambiguous, though.

Just adding "val" and "val2" to the parenthenticals removes any confusion
if you are quickly skimming the text?

There is still the degenerate case of val==0 and val2==INT_MAX which is
equivalent to FUTEX_WAKE followed by an atomic FUTEX_WAIT since all
waiters move queues and no waiter is officially woken and allowed to
return to userspace?

-- 
Cheers,
Carlos.