On Mon, Dec 13, 2021 at 08:09:22AM +0000, Woodhouse, David wrote: > 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> Queued for further review and testing. To Frederic's point, this won't go to mainline unless it is actually needed, but it will at least be pulled into a branch in -rcu marked with a tag for future reference. Thanx, Paul
