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

["Onur Özkan" <work@onurozkan.dev>]

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:

	"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?"

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.
> 
> Best,
> Gary
> 
> >  #ifndef CONFIG_TINY_SRCU
> >  int init_srcu_struct_fast(struct srcu_struct *ssp);
> >  int init_srcu_struct_fast_updown(struct srcu_struct *ssp);
> > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> > index 625921e27dfb..f3562d3b3888 100644
> > --- a/rust/helpers/helpers.c
> > +++ b/rust/helpers/helpers.c
> > @@ -88,6 +88,7 @@
> >  #include "signal.c"
> >  #include "slab.c"
> >  #include "spinlock.c"
> > +#include "srcu.c"
> >  #include "sync.c"
> >  #include "task.c"
> >  #include "time.c"
> > diff --git a/rust/helpers/srcu.c b/rust/helpers/srcu.c
> > new file mode 100644
> > index 000000000000..225b3bf9334a
> > --- /dev/null
> > +++ b/rust/helpers/srcu.c
> > @@ -0,0 +1,30 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/srcu.h>
> > +
> > +__rust_helper int rust_helper_init_srcu_struct_with_key(struct srcu_struct *ssp,
> > +							const char *name,
> > +							struct lock_class_key *key)
> > +{
> > +	return __init_srcu_struct(ssp, name, key);
> > +}
> > +
> > +__rust_helper int rust_helper_srcu_read_lock(struct srcu_struct *ssp)
> > +{
> > +	return srcu_read_lock(ssp);
> > +}
> > +
> > +__rust_helper void rust_helper_srcu_read_unlock(struct srcu_struct *ssp, int idx)
> > +{
> > +	srcu_read_unlock(ssp, idx);
> > +}
> > +
> > +__rust_helper void rust_helper_srcu_barrier(struct srcu_struct *ssp)
> > +{
> > +	srcu_barrier(ssp);
> > +}
> > +
> > +__rust_helper void rust_helper_synchronize_srcu_expedited(struct srcu_struct *ssp)
> > +{
> > +	synchronize_srcu_expedited(ssp);
> > +}
> 
>