Messages in this thread | | | Date | Wed, 2 Mar 2016 14:37:18 +0800 | From | Boqun Feng <> | Subject | Re: [RFC v2 0/6] Track RCU dereferences in RCU read-side critical sections |
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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 [unhandled content-type:application/pgp-signature] | |