On Mon, 2021-12-13 at 12:30 +0530, Neeraj Upadhyay wrote: > To support onlining multiple CPUs concurrently, > change rcu_state.n_online_cpus updates to be atomic. > Note, it's ok for rcu_blocking_is_gp() to do a > atomic_read(&rcu_state.n_online_cpus), as the > value of .n_online_cpus switches from 1->2, in > rcutree_prepare_cpu(), which runs before the new > CPU comes online. Similarly 2->1 transition happens > from rcutree_dead_cpu(), which executes after the > CPU is offlined, and runs on the last online CPU. > > Signed-off-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx> In my parallel-bringup series, the prepare stages are still being executed in series on the BSP, so I don't think this patch is needed yet. I'm not sure we'd ever end up with the prepare stages being done in parallel — the most I see us doing is onlining a single *batch* of CPUs at a time, much like bringup_nonboot_cpus() does. But this patch certainly doesn't *hurt*. Acked-by: David Woodhouse <dwmw@xxxxxxxxxxxx> Amazon Development Centre (London) Ltd. Registered in England and Wales with registration number 04543232 with its registered office at 1 Principal Place, Worship Street, London EC2A 2FA, United Kingdom.
