linux-kernel - Re: [RFC v2 0/6] Track RCU dereferences in RCU read-side critical sections

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Message-ID: <20160301100134.GW6375@twins.programming.kicks-ass.net>
Date:	Tue, 1 Mar 2016 11:01:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>, sasha.levin@...cle.com
Subject: Re: [RFC v2 0/6] Track RCU dereferences in RCU read-side critical
 sections

On Tue, Mar 01, 2016 at 10:57:07AM +0100, Peter Zijlstra wrote:
> On Tue, Mar 01, 2016 at 05:32:42PM +0800, Boqun Feng wrote:
> > > One could for example allow something like:
> > > 
> > > 	rcu_read_lock();
> > > 	rcu_annotate(&var->field);
> > > 
> > > 	foo();
> > > 
> > > 	rcu_read_unlock();
> > > 
> > > As an alternative to the syntax suggested by Ingo. This would allow
> > > keeping the existing rcu_read_lock() signature so you don't have to
> > > force update the entire kernel at once, while also (easily) allowing
> > > multiple variables. Like:
> > > 
> > > 	rcu_read_lock();
> > > 	rcu_annotate(&var->field);
> > > 	rcu_annotate(&var2->field2);
> > > 
> > > You can then have a special rule that if a particular RCU section has an
> > > annotation, any rcu_dereference() not matched will field a warning. If
> > > the annotation section is empty, nothing.
> > > 
> > 
> > Good idea! but I don't think annotating a field in C language is easy,
> > I will try to see what we can get. Do you have something already in your
> > mind?
> 
> No, didn't really think about that :-/ The most restrictive version is
> taking the absolute address, but that would make things like actual data
> structures impossible.

So the thing with locks is they get a struct lockdep_map added, in which
we store all kinds of useful. But I don't think we cannot add a similar
structure to each and every RCU dereferencable (is that a word?)
variable.