On Fri, May 29, 2026 at 04:39:52PM +0300, Onur Özkan wrote:
> This is needed by rust/helpers/srcu.c which now adds
> rust_helper_srcu_readers_active() as a wrapper around the SRCU helper
> for Rust callers.
>
> To achive this:
>
> 1- Move the srcu_readers_active() implementation from
> "kernel/rcu/srcutree.c" to "include/linux/srcutree.h".
>
> 2- Implement a matching srcu_readers_active() in
> "include/linux/srcutiny.h" and use it on the existing open-coded
> WARN_ON() check in cleanup_srcu_struct().
>
> Reviewed-by: Gary Guo <[email protected]>
> Reviewed-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Onur Özkan <[email protected]>
It would be good to merge the rust/helpers piece of this change into
the separate commit that I suggested for patch 1/4. Either way, I
still stand behind my Reviewed-by.
Thanx, Paul
> ---
> include/linux/srcutiny.h | 13 +++++++++++++
> include/linux/srcutree.h | 24 ++++++++++++++++++++++++
> kernel/rcu/srcutiny.c | 2 +-
> kernel/rcu/srcutree.c | 25 -------------------------
> rust/helpers/srcu.c | 5 +++++
> 5 files changed, 43 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
> index 905b629e8fa3..fbcf13bc12d1 100644
> --- a/include/linux/srcutiny.h
> +++ b/include/linux/srcutiny.h
> @@ -154,4 +154,17 @@ static inline void srcu_torture_stats_print(struct
> srcu_struct *ssp,
> data_race(READ_ONCE(ssp->srcu_idx_max)));
> }
>
> +/**
> + * srcu_readers_active - returns true if there are readers. and false
> otherwise.
> + * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
> + *
> + * Note that this is not an atomic primitive, and can therefore suffer
> + * severe errors when invoked on an active srcu_struct. That said, it
> + * can be useful as an error check at cleanup time.
> + */
> +static inline bool srcu_readers_active(struct srcu_struct *ssp)
> +{
> + return READ_ONCE(ssp->srcu_lock_nesting[0]) ||
> READ_ONCE(ssp->srcu_lock_nesting[1]);
> +}
> +
> #endif
> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> index fd1a9270cb9a..75e54e4f963f 100644
> --- a/include/linux/srcutree.h
> +++ b/include/linux/srcutree.h
> @@ -374,4 +374,28 @@ static inline void srcu_check_read_flavor(struct
> srcu_struct *ssp, int read_flav
> __srcu_check_read_flavor(ssp, read_flavor);
> }
>
> +/**
> + * srcu_readers_active - returns true if there are readers. and false
> otherwise.
> + * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
> + *
> + * Note that this is not an atomic primitive, and can therefore suffer
> + * severe errors when invoked on an active srcu_struct. That said, it
> + * can be useful as an error check at cleanup time.
> + */
> +static inline bool srcu_readers_active(struct srcu_struct *ssp)
> +{
> + int cpu;
> + unsigned long sum = 0;
> +
> + for_each_possible_cpu(cpu) {
> + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
> +
> + sum += atomic_long_read(&sdp->srcu_ctrs[0].srcu_locks);
> + sum += atomic_long_read(&sdp->srcu_ctrs[1].srcu_locks);
> + sum -= atomic_long_read(&sdp->srcu_ctrs[0].srcu_unlocks);
> + sum -= atomic_long_read(&sdp->srcu_ctrs[1].srcu_unlocks);
> + }
> + return sum;
> +}
> +
> #endif
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 780a95e8cad7..dde99876d473 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -85,7 +85,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct_generic);
> */
> void cleanup_srcu_struct(struct srcu_struct *ssp)
> {
> - WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
> + WARN_ON(srcu_readers_active(ssp));
> irq_work_sync(&ssp->srcu_irq_work);
> flush_work(&ssp->srcu_work);
> WARN_ON(ssp->srcu_gp_running);
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 45154630c54e..d1a69320b5c0 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -599,31 +599,6 @@ static bool srcu_readers_active_idx_check(struct
> srcu_struct *ssp, int idx)
> return srcu_readers_lock_idx(ssp, idx, did_gp, unlocks);
> }
>
> -/**
> - * srcu_readers_active - returns true if there are readers. and false
> - * otherwise
> - * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
> - *
> - * Note that this is not an atomic primitive, and can therefore suffer
> - * severe errors when invoked on an active srcu_struct. That said, it
> - * can be useful as an error check at cleanup time.
> - */
> -static bool srcu_readers_active(struct srcu_struct *ssp)
> -{
> - int cpu;
> - unsigned long sum = 0;
> -
> - for_each_possible_cpu(cpu) {
> - struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
> -
> - sum += atomic_long_read(&sdp->srcu_ctrs[0].srcu_locks);
> - sum += atomic_long_read(&sdp->srcu_ctrs[1].srcu_locks);
> - sum -= atomic_long_read(&sdp->srcu_ctrs[0].srcu_unlocks);
> - sum -= atomic_long_read(&sdp->srcu_ctrs[1].srcu_unlocks);
> - }
> - return sum;
> -}
> -
> /*
> * We use an adaptive strategy for synchronize_srcu() and especially for
> * synchronize_srcu_expedited(). We spin for a fixed time period
> diff --git a/rust/helpers/srcu.c b/rust/helpers/srcu.c
> index 225b3bf9334a..1a2f563640e0 100644
> --- a/rust/helpers/srcu.c
> +++ b/rust/helpers/srcu.c
> @@ -9,6 +9,11 @@ __rust_helper int
> rust_helper_init_srcu_struct_with_key(struct srcu_struct *ssp,
> return __init_srcu_struct(ssp, name, key);
> }
>
> +__rust_helper bool rust_helper_srcu_readers_active(struct srcu_struct *ssp)
> +{
> + return srcu_readers_active(ssp);
> +}
> +
> __rust_helper int rust_helper_srcu_read_lock(struct srcu_struct *ssp)
> {
> return srcu_read_lock(ssp);
> --
> 2.51.2
>
