On Mon, Dec 11, 2023 at 09:04:04PM +0100, Frederic Weisbecker wrote: > Le Mon, Dec 11, 2023 at 08:38:59AM -0800, Paul E. McKenney a écrit : > > On Fri, Dec 08, 2023 at 11:05:37PM +0100, Frederic Weisbecker wrote: > > > TREE04 can trigger a writer stall if run with memory pressure. This > > > is due to a circular dependency between waiting for expedited grace > > > period and polling on expedited grace period when workqueues go back > > > to mayday serialization. > > > > > > Here is a proposal fix. > > > > The torture.sh "acceptance test" with KCSAN and --duration 30 ran > > fine except for this in TREE09: > > > > kernel/rcu/tree_nocb.h:1785:13: error: unused function '__call_rcu_nocb_wake' [-Werror,-Wunused-function] > > > > My guess is that the declaration of __call_rcu_nocb_wake() in > > kernel/rcu/tree.h needs an "#ifdef CONFIG_SMP", but you might have a > > better fix. > > Could be because if CONFIG_RCU_NO_CB_CPU=n, the function is only called > (though as dead code) from rcutree_migrate_callbacks() which in turn only > exists if CONFIG_HOTPLUG_CPU=y. > > Something like that then: > > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h > index 35f7af331e6c..e1ff53d5084c 100644 > --- a/kernel/rcu/tree.h > +++ b/kernel/rcu/tree.h > @@ -445,6 +445,8 @@ static void rcu_qs(void); > static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); > #ifdef CONFIG_HOTPLUG_CPU > static bool rcu_preempt_has_tasks(struct rcu_node *rnp); > +static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, > + unsigned long flags); > #endif /* #ifdef CONFIG_HOTPLUG_CPU */ > static int rcu_print_task_exp_stall(struct rcu_node *rnp); > static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); > @@ -466,8 +468,6 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, > unsigned long j, bool lazy); > static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head, > rcu_callback_t func, unsigned long flags, bool lazy); > -static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, > - unsigned long flags); > static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); > static bool do_nocb_deferred_wakeup(struct rcu_data *rdp); > static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); This one passes TREE01 and TINY01, but on TREE09 still gets this: kernel/rcu/tree_nocb.h:1785:13: error: ‘__call_rcu_nocb_wake’ defined but not used [-Werror=unused-function] Huh. I suppose that there is always __maybe_unused? Thanx, Paul
