On Fri, Sep 08, 2023 at 10:35:58PM +0200, Frederic Weisbecker wrote: > rcu_report_dead() is the last RCU word from the CPU down through the > hotplug path. It is called in the idle loop right before the CPU shuts > down for good. Because it removes the CPU from the grace period state > machine and reports an ultimate quiescent state if necessary, no further > use of RCU is allowed. Therefore it is expected that IRQs are disabled > upon calling this function and are not to be re-enabled again until the > CPU shuts down. > > Remove the IRQs disablement from that function and verify instead that > it is actually called with IRQs disabled as it is expected at that > special point in the idle path. > > Reviewed-by: Joel Fernandes (Google) <[email protected]> > Signed-off-by: Frederic Weisbecker <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]> > --- > kernel/rcu/tree.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index a83ecab77917..8b5ebef32e17 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4553,11 +4553,16 @@ void rcu_cpu_starting(unsigned int cpu) > */ > void rcu_report_dead(unsigned int cpu) > { > - unsigned long flags, seq_flags; > + unsigned long flags; > unsigned long mask; > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ > > + /* > + * IRQS must be disabled from now on and until the CPU dies, or an > interrupt > + * may introduce a new READ-side while it is actually off the QS masks. > + */ > + lockdep_assert_irqs_disabled(); > // Do any dangling deferred wakeups. > do_nocb_deferred_wakeup(rdp); > > @@ -4565,7 +4570,6 @@ void rcu_report_dead(unsigned int cpu) > > /* Remove outgoing CPU from mask in the leaf rcu_node structure. */ > mask = rdp->grpmask; > - local_irq_save(seq_flags); > arch_spin_lock(&rcu_state.ofl_lock); > raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order > guarantee. */ > rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq); > @@ -4579,8 +4583,6 @@ void rcu_report_dead(unsigned int cpu) > WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask); > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > arch_spin_unlock(&rcu_state.ofl_lock); > - local_irq_restore(seq_flags); > - > rdp->cpu_started = false; > } > > -- > 2.41.0 >
