Re: bug in futex.2, FUTEX_CMP_REQUEUE

["Jₑₙₛ Gustedt" <jens.gustedt@inria.fr>]

Hello again,

On Tue, 27 May 2025 08:12:41 -0400, Carlos O'Donell wrote:

> > 	    Fixes: 3dfcc11d4630 (2015-12-15; "futex.2: Expand
> > description of FUTEX_CMP_REQUEUE") Fixes: 8297383e9eeb (2015-12-15;
> > "futex.2: Clean-ups and FIXME removeal after feedback from Thomas
> > Gleixner") Reported-by: Jens Gustedt <jens.gustedt@inria.fr>
> > Signed-off-by: Alejandro Colomar <alx@kernel.org>
> > 
> > 	diff --git a/man/man2/futex.2 b/man/man2/futex.2
> > 	index 128612ee1..9a15a0fdb 100644
> > 	--- a/man/man2/futex.2
> > 	+++ b/man/man2/futex.2
> > 	@@ -501,7 +501,7 @@ .SS Futex operations
> > 	 (Specifying the argument as 0 is not useful, because it
> > would make the .B FUTEX_CMP_REQUEUE
> > 	 operation equivalent to
> > 	-.BR FUTEX_WAIT .)
> > 	+.BR FUTEX_WAKE .)  
> 
> This is incorrect.
> 
> A value of zero means no tasks are woken.

No, `val2 == 0` means that as many as specified in `val` are woken,
and that no task additionally is queued on `uaddr2`. So this is
definitively a wake operation.

The resulting text is then not completely correct, because it is
missing the tests for `val3` but at least is a bit closer to reality
than before.

Thanks
Jₑₙₛ


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