On 10/31/24 13:39, Andrew Jones wrote:
> It's reasonable for users of on_cpu() and on_cpumask() to assume
> they can read data that 'func' has written when the call completes.
> Ensure the caller doesn't observe a completion (target cpus are again
> idle) without also being able to observe any writes which were made
> by func(). Do so by adding barriers to implement the following
>
> target-cpu calling-cpu
> ---------- -----------
> func() /* store something */ /* wait for target to be idle */
> smp_wmb(); smp_rmb();
> set_cpu_idle(smp_processor_id(), true); /* load what func() stored */
>
> Signed-off-by: Andrew Jones <andrew.jones@xxxxxxxxx>
Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
Eric
> ---
> lib/on-cpus.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/lib/on-cpus.c b/lib/on-cpus.c
> index f6072117fa1b..356f284be61b 100644
> --- a/lib/on-cpus.c
> +++ b/lib/on-cpus.c
> @@ -79,6 +79,7 @@ void do_idle(void)
> smp_wait_for_event();
> smp_rmb();
> on_cpu_info[cpu].func(on_cpu_info[cpu].data);
> + smp_wmb(); /* pairs with the smp_rmb() in on_cpu() and on_cpumask() */
> }
> }
>
> @@ -145,12 +146,14 @@ void on_cpumask(const cpumask_t *mask, void (*func)(void *data), void *data)
> smp_wait_for_event();
> for_each_cpu(cpu, mask)
> cpumask_clear_cpu(me, &on_cpu_info[cpu].waiters);
> + smp_rmb(); /* pairs with the smp_wmb() in do_idle() */
> }
>
> void on_cpu(int cpu, void (*func)(void *data), void *data)
> {
> on_cpu_async(cpu, func, data);
> cpu_wait(cpu);
> + smp_rmb(); /* pairs with the smp_wmb() in do_idle() */
> }
>
> void on_cpus(void (*func)(void *data), void *data)
