On Tue, Jun 20, 2023 at 09:15:03AM -0700, Alexei Starovoitov wrote:
> On Mon, Jun 19, 2023 at 7:00 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
> >
> > +static void bpf_rcu_gp_acc_work(struct callback_head *head)
> > +{
> > + struct bpf_rcu_gp_acc_ctx *ctx = container_of(head, struct bpf_rcu_gp_acc_ctx, work);
> > +
> > + local_irq_disable();
> > + rcu_momentary_dyntick_idle();
> > + local_irq_enable();
>
> We discussed this with Paul off-line and decided to go a different route.
> Paul prepared a patch for us to expose rcu_request_urgent_qs_task().
> I'll be sending the series later this week.
Just for completeness, this patch is in -rcu here and as shown below:
b1edaa1e6364 ("rcu: Export rcu_request_urgent_qs_task()")
Thanx, Paul
------------------------------------------------------------------------
commit b1edaa1e6364caf9833a30b5dd7599080b6806b8
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Thu Jun 8 16:31:49 2023 -0700
rcu: Export rcu_request_urgent_qs_task()
If a CPU is executing a long series of non-sleeping system calls,
RCU grace periods can be delayed for on the order of a couple hundred
milliseconds. This is normally not a problem, but if each system call
does a call_rcu(), those callbacks can stack up. RCU will eventually
notice this callback storm, but use of rcu_request_urgent_qs_task()
allows the code invoking call_rcu() to give RCU a heads up.
This function is not for general use, not yet, anyway.
Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 7f17acf29dda..7b949292908a 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -138,6 +138,8 @@ static inline int rcu_needs_cpu(void)
return 0;
}
+static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
+
/*
* Take advantage of the fact that there is only one CPU, which
* allows us to ignore virtualization-based context switches.
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 56bccb5a8fde..126f6b418f6a 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -21,6 +21,7 @@ void rcu_softirq_qs(void);
void rcu_note_context_switch(bool preempt);
int rcu_needs_cpu(void);
void rcu_cpu_stall_reset(void);
+void rcu_request_urgent_qs_task(struct task_struct *t);
/*
* Note a virtualization-based context switch. This is simply a
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 9829d8161b21..0c99ec19c8e0 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -493,7 +493,6 @@ static inline void rcu_expedite_gp(void) { }
static inline void rcu_unexpedite_gp(void) { }
static inline void rcu_async_hurry(void) { }
static inline void rcu_async_relax(void) { }
-static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
#else /* #ifdef CONFIG_TINY_RCU */
bool rcu_gp_is_normal(void); /* Internal RCU use. */
bool rcu_gp_is_expedited(void); /* Internal RCU use. */
@@ -514,7 +513,6 @@ struct task_struct *get_rcu_tasks_rude_gp_kthread(void);
#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
static inline void show_rcu_tasks_gp_kthreads(void) {}
#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
-void rcu_request_urgent_qs_task(struct task_struct *t);
#endif /* #else #ifdef CONFIG_TINY_RCU */
#define RCU_SCHEDULER_INACTIVE 0
