Messages in this thread Patch in this message | | | Date | Mon, 27 Jun 2022 14:16:58 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu: Add a warnings in sync_sched_exp_online_cleanup() |
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On Wed, Jun 22, 2022 at 11:43:26PM +0000, Zhang, Qiang1 wrote: > > 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@intel.com> > --- > 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().
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 >
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