> > Add Cc > > Currently, the sync_sched_exp_online_cleanup() is invoked in > cpuhp per-cpu kthreads when CPU is going online, so the CPU id > obtained by get_cpu() should always be equal to the CPU id of > the passed parameter, that is to say, the smp_call_function_single() > never be invoked, if be invoked, there may be problem with cpu-hotplug, > this commit add WARN_ON_ONCE() to remind everyone. > > Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx> > --- > kernel/rcu/tree_exp.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index be667583a554..ae8dcfd4486c 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -865,6 +865,8 @@ static void sync_sched_exp_online_cleanup(int cpu) > put_cpu(); > return; > } > + > + WARN_ON_ONCE(my_cpu != cpu); >If we are going to add this sort of warning, why not instead add it >to rcutree_online_cpu()? > >The reason the warning has not been present is the prospect of concurrent >onlining at boot time, which might have rcutree_online_cpu() invoked >from CPU 0 for multiple CPUs at boot. However, the for_each_online_cpu() >loop has recently been removed from rcu_init(). The rcutree_online_cpu() is always invoked in per-cpu cpuhp kthreads, and even if it is called directly through the for_each_online_cpu() loop in rcu_init(), since the rcu_init() takes precedence over smp initialization, only the CPU0 is online at this time, still only called on CPU0. Thanks Zqiang > >But I would like to hear what others think. Would such a warning >significantly help debugging? > > Thanx, Paul > > /* Quiescent state needed on some other CPU, send IPI. */ > ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); > put_cpu(); > -- > 2.25.1 >
