On Mon, Jan 08, 2018 at 07:42:11PM -0800, Tejun Heo wrote:
> Hello, Paul.
>
> On Mon, Jan 08, 2018 at 04:31:27PM -0800, Paul E. McKenney wrote:
> > +static int __init rcu_init_wq_rescuer(void)
> > +{
> > + WARN_ON(init_rescuer(rcu_gp_workqueue));
> > + return 0;
> > +}
> > +core_initcall(rcu_init_wq_rescuer);
>
> So, what I don't get is why RCU needs to call this explicitly.
> core_initcall() is after workqueue_init() anyway. Why am I missing?
Me being stupid, I guess.
OK, so I can put WQ_MEM_RECLAIM on the early boot creation of RCU's
workqueue_struct as shown below, right?
Thanx, Paul
------------------------------------------------------------------------
commit 9884a945a65837cda6de2ff621d47c59a6ca3e28
Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Date: Mon Jan 8 14:35:52 2018 -0800
rcu: Create RCU-specific workqueues with rescuers
RCU's expedited grace periods can participate in out-of-memory deadlocks
due to all available system_wq kthreads being blocked and there not being
memory available to create more. This commit prevents such deadlocks
by allocating an RCU-specific workqueue_struct at early boot time, and
providing it with a rescuer to ensure forward progress. This uses the
shiny new init_rescuer() function provided by Tejun (but indirectly).
This commit also causes SRCU to use this new RCU-specific
workqueue_struct. Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint.
Reported-by: Prateek Sood <prs...@codeaurora.org>
Reported-by: Tejun Heo <t...@kernel.org>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 59c471de342a..acabc4781b08 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -493,6 +493,7 @@ void show_rcu_gp_kthreads(void);
void rcu_force_quiescent_state(void);
void rcu_bh_force_quiescent_state(void);
void rcu_sched_force_quiescent_state(void);
+extern struct workqueue_struct *rcu_gp_workqueue;
#endif /* #else #ifdef CONFIG_TINY_RCU */
#ifdef CONFIG_RCU_NOCB_CPU
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 6d5880089ff6..89f0f6b3ce9a 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -465,7 +465,7 @@ static bool srcu_queue_delayed_work_on(int cpu, struct
workqueue_struct *wq,
*/
static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay)
{
- srcu_queue_delayed_work_on(sdp->cpu, system_power_efficient_wq,
+ srcu_queue_delayed_work_on(sdp->cpu, rcu_gp_workqueue,
&sdp->work, delay);
}
@@ -664,7 +664,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *sp,
struct srcu_data *sdp,
rcu_seq_state(sp->srcu_gp_seq) == SRCU_STATE_IDLE) {
WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq,
sp->srcu_gp_seq_needed));
srcu_gp_start(sp);
- queue_delayed_work(system_power_efficient_wq, &sp->work,
+ queue_delayed_work(rcu_gp_workqueue, &sp->work,
srcu_get_delay(sp));
}
raw_spin_unlock_irqrestore_rcu_node(sp, flags);
@@ -1198,7 +1198,7 @@ static void srcu_reschedule(struct srcu_struct *sp,
unsigned long delay)
raw_spin_unlock_irq_rcu_node(sp);
if (pushgp)
- queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
+ queue_delayed_work(rcu_gp_workqueue, &sp->work, delay);
}
/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f9c0ca2ccf0c..d658538e6f7d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4272,6 +4272,8 @@ static void __init rcu_dump_rcu_node_tree(struct
rcu_state *rsp)
pr_cont("\n");
}
+struct workqueue_struct *rcu_gp_workqueue;
+
void __init rcu_init(void)
{
int cpu;
@@ -4298,6 +4300,10 @@ void __init rcu_init(void)
rcu_cpu_starting(cpu);
rcutree_online_cpu(cpu);
}
+
+ /* Create workqueue for expedited GPs and for Tree SRCU. */
+ rcu_gp_workqueue = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
+ WARN_ON(!rcu_gp_workqueue);
}
#include "tree_exp.h"
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 46d61b597731..3ba3ef4d4796 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -606,7 +606,7 @@ static void _synchronize_rcu_expedited(struct rcu_state
*rsp,
rew.rew_rsp = rsp;
rew.rew_s = s;
INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
- schedule_work(&rew.rew_work);
+ queue_work(rcu_gp_workqueue, &rew.rew_work);
}
/* Wait for expedited grace period to complete. */
