Re: [PATCH v8 1/4] rust: helpers: add SRCU helpers

["Onur Özkan" <work@onurozkan.dev>]

On Fri, 29 May 2026 13:16:17 +0100
Gary Guo <gary@garyguo.net> wrote:

> On Fri May 29, 2026 at 1:07 PM BST, Onur Özkan wrote:
> > On Fri, 29 May 2026 12:58:17 +0100
> > Gary Guo <gary@garyguo.net> wrote:
> >
> >> On Fri May 29, 2026 at 12:43 PM BST, Onur Özkan wrote:
> >> > Add helper wrappers for SRCU functions that are exposed to Rust
> >> > through generated bindings.
> >> >
> >> > Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> >> > Signed-off-by: Onur Özkan <work@onurozkan.dev>
> >> > ---
> >> >  include/linux/srcu.h   |  5 +++++
> >> >  rust/helpers/helpers.c |  1 +
> >> >  rust/helpers/srcu.c    | 30 ++++++++++++++++++++++++++++++
> >> >  3 files changed, 36 insertions(+)
> >> >  create mode 100644 rust/helpers/srcu.c
> >> >
> >> > diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> >> > index 81b1938512d5..790a4ef713c0 100644
> >> > --- a/include/linux/srcu.h
> >> > +++ b/include/linux/srcu.h
> >> > @@ -57,6 +57,11 @@ int __init_srcu_struct_fast_updown(struct srcu_struct *ssp, const char *name,
> >> >  #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
> >> >  
> >> >  int init_srcu_struct(struct srcu_struct *ssp);
> >> > +static inline int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
> >> > +				     struct lock_class_key *key)
> >> > +{
> >> > +	return init_srcu_struct(ssp);
> >> > +}
> >> 
> >> 
> >> This looks like a different strategy than, say, how mutex handles lockdep. IMO
> >> the way that mutex handles this is more clear.
> >
> > Initially it was the same strategy, this one was suggested by Paul [1] and it
> > didn't sound like a bad idea to me. Also, in previous revisions, Boqun once
> > said:
> 
> I'm talking about changing how this is handled in SRCU side, not helper side.
> 
> >
> > 	"Having a "#ifdef" in a function body is generally considered as bad code
> > 	(I know we have some of these in rust helpers, but helpers are a bit
> > 	special and maybe we should clean them up). So could you move this
> > 	function into include/linux/srcutiny.h and include/linux/srcutree.h?"
> 
> mutex.h doesn't use ifdef inside function body, it just define two static inline
> functions with the same signature in different ifdef branches.
> 

I might have confused them, let me check them again.

Thanks,
Onur

> Best,
> Gary
> 
> >
> > So putting them together, I decided to follow Paul's suggestion.
> >
> > [1]: https://lore.kernel.org/all/05906890-cf06-414c-a625-02f9d7150d57@paulmck-laptop
> >
> >> 
> >> If we follow the way mutex is handles this, the `init_srcu_struct` would always
> >> create lock class key and forward to `__init_srcu_struct`, and
> >> `__init_srcu_struct` is an inline function that either calls
> >> `init_srcu_struct_lockdep` with all args, or discard name/key and forward to
> >> `init_srcu_struct_mutex`.
> >> 
> >> This is beneficial because the usage flows one way. You don't have in one config
> >> `init_srcu_struct` call `__init_srcu_struct` and have the opposite in another
> >> config, which I think can be quite confusing.