On Tue, Mar 01, 2016 at 11:01:34AM +0100, Peter Zijlstra wrote: > 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. >
Another problem of taking the absolute address is the address may change
from rcu_annotate() to rcu_dereference() for example:
rcu_read_lock();
rcu_annotate(&var->field);
// in another thread
var = new_var;
// the address of var->field is different now.
rcu_dereference(var->field);
rcu_read_unlock();
> 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.
>
Well, some of them have rcu_head, but not all.. so you're right.
>
I come up with something you may not like ;-) , which is taking the
strings of the expressions, for example:
rcu_read_lock();
rcu_annotate(var->field); // "var->field" is added for
// the current section
rcu_dereference(var->field); // OK, because the expression
// "var->field" is annotated.
rcu_dereference(var->field2); // Not OK, because the
// expression "var->field2" is
// not annotated, nor is any of
// its suffix.
rcu_annotate(field3); // "field3" is added for the
// current section
rcu_dereference(var2->field3); // OK, because the suffix
// "field3" is annotated.
rcu_read_unlock();
I think this is more accurate than taking the absolute address because
the address changing situations exist. So.. thoughts?
Regards,
Boqun
signature.asc
Description: PGP signature
