On Mon, Jul 08, 2024 at 11:12:49AM +0200, Peter Zijlstra wrote:
> In order to support carrying an srcu_read_lock() section across fork,
> where both the parent and child process will do: srcu_read_unlock(),
> it is needed to account for the extra decrement with an extra
> increment at fork time.
>
We also need to dup the per-task lock held stack in order to maintain
consistent data for lockdep, right?
Regards,
Boqun
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> include/linux/srcu.h | 1 +
> include/linux/srcutiny.h | 10 ++++++++++
> kernel/rcu/srcutree.c | 5 +++++
> 3 files changed, 16 insertions(+)
>
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -55,6 +55,7 @@ void call_srcu(struct srcu_struct *ssp,
> void (*func)(struct rcu_head *head));
> void cleanup_srcu_struct(struct srcu_struct *ssp);
> int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
> +void __srcu_clone_read_lock(struct srcu_struct *ssp, int idx);
> void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
> void synchronize_srcu(struct srcu_struct *ssp);
> unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
> --- a/include/linux/srcutiny.h
> +++ b/include/linux/srcutiny.h
> @@ -71,6 +71,16 @@ static inline int __srcu_read_lock(struc
> return idx;
> }
>
> +static inline void __srcu_clone_read_lock(struct srcu_struct *ssp, int idx)
> +{
> + int newval;
> +
> + preempt_disable(); // Needed for PREEMPT_AUTO
> + newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1;
> + WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
> + preempt_enable();
> +}
> +
> static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
> {
> synchronize_srcu(ssp);
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -720,6 +720,11 @@ int __srcu_read_lock(struct srcu_struct
> }
> EXPORT_SYMBOL_GPL(__srcu_read_lock);
>
> +void __srcu_clone_read_lock(struct srcu_struct *ssp, int idx)
> +{
> + this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
> +}
> +
> /*
> * Removes the count for the old reader from the appropriate per-CPU
> * element of the srcu_struct. Note that this may well be a different
>
>