linux-kernel - Re: [RFC tip/locking/lockdep v5 05/17] lockdep: Extend __bfs() to work with multiple kinds of dependencies

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180222163120.zhytq7yezny4e7mj@tardis>
Date:   Fri, 23 Feb 2018 00:31:20 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andrea Parri <parri.andrea@...il.com>
Subject: Re: [RFC tip/locking/lockdep v5 05/17] lockdep: Extend __bfs() to
 work with multiple kinds of dependencies

On Thu, Feb 22, 2018 at 04:51:43PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 22, 2018 at 04:30:34PM +0100, Peter Zijlstra wrote:
> > On Thu, Feb 22, 2018 at 11:12:10PM +0800, Boqun Feng wrote:
> > > On Thu, Feb 22, 2018 at 03:26:14PM +0100, Peter Zijlstra wrote:
> > 
> > > > However, I would suggest:
> > > > 
> > > > static inline bool is_xr(u16 dep)
> > > > {
> > > > 	return !!(dep & (DEP_NR_MASK | DEP_RR_MASK));
> > > > }
> > > > 
> > > > static inline bool is_rx(u16 dep)
> > > > {
> > > > 	return !!(dep & (DEP_RN_MASK | DEP_RR_MASK));
> > > > }
> > > > 
> > > > 		/* Skip *R -> R* relations */
> > > > 		if (have_xr && is_rx(entry->dep))
> > > > 			continue;
> > > 
> > > I don't think this works, if we pick a *R for previous entry, and for
> > > current entry, we have RR, NN and NR, your approach will skip the
> > > current entry, but actually we can pick NN or NR (of course, in __bfs(),
> > > we can greedily pick NN, because if NR causes a deadlock, so does NN).
> > 
> > I don't get it, afaict my suggestion is identical.
> > 
> > You skip condition: pick_dep() < 0, evaluates to:
> > 
> > 	is_rr && (!NN_MASK && !NR_MASK) :=
> > 	is_rr && (RN_MASK | RR_MASK)
> > 
> > Which is exactly what I have.
> 
> Ooh, I think I see what I did wrong, would something like:
> 
> 	if (have_xr && !is_nx(entry-dep))
> 
> work? That's a lot harder to argue about though, still much better than

I think it works. Although I prefer use name "has_nx" for the fucntion.

> that tri-state pick thing.
> 

Agree.

> > If that is satisfied, you set entry->is_rr to pick_dep(), which his
> > harder to evaluate, but is something like:
> > 
> > 	is_rr && NR_MASK || !(NN_MASK | RN_MASK) :=

If is_rr is true and NN_MASK is true, pick_dep() will return 0, however,
your expression will return NR_MASK.

	entry->have_xr = !(has_nn(entry->dep) || (!is_rr && has_rn(entry->dep)));
	              := !has_nn(entry->dep) && (is_rr || !has_rn(entry->dep))

Regards,
Boqun

> > 	is_rr && NR_MASK || (NR_MASK | RR_MASK) :=
> > 	(NR_MASK | RR_MASK)
> > 
> > (because is_rr && RR_MASK will have been skipped)
> > 
> > > > 
> > > > 		entry->have_xr = is_xr(entry->dep);
> 
> This one I think is still correct though.

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)