Re: [PATCH v9 00/11] futex: Add support task local hash maps.

[Peter Zijlstra]

On Mon, Mar 10, 2025 at 05:27:10PM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-03-10 17:01:02 [+0100], Peter Zijlstra wrote:
> > On Wed, Mar 05, 2025 at 10:02:37AM +0100, Sebastian Andrzej Siewior wrote:
> > > On 2025-03-04 15:58:39 [+0100], To Peter Zijlstra wrote:
> > > > hash. That is why I had the `released' member.
> > > 
> > > The box was still alive this morning so it did survive >12h testing. I
> > > would bring back the `released' member back unless you have other
> > > preferences.
> > 
> > Like I just wrote in that other email; I'm a bit confused as to how this
> > can happen. If rcuref_put() returns success, then the value is DEAD. It must
> > then either be decremented below RELEASED or incremented past NOREF in
> > order for rcuref_read() to no longer return 0.
> 
> We can't rely on 0 to be released as it might become active. We could
> change rcuref_read() to return 0 if it could be obtained and -1 if it
> can not.
> We don't have many users atm so an audit should be quick.

Right, so I failed to understand initially. When DEAD it stays 0, but
there is indeed the one case where it isn't yet DEAD but still returns
0.

Making the DEAD return -1 seems like a good solution.