Re: [PATCH] cgroup/cpuset: fix circular locking dependency
From: Paul E. McKenney <hidden>
Date: 2018-01-09 04:19:41
Also in:
lkml
Subsystem:
read-copy update (rcu), sleepable read-copy update (srcu), the rest · Maintainers:
"Paul E. McKenney", Frederic Weisbecker, Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng, Uladzislau Rezki, Lai Jiangshan, Linus Torvalds
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:quoted
+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 [off-list ref]
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 [off-list ref]
Reported-by: Tejun Heo [off-list ref]
Signed-off-by: Paul E. McKenney [off-list ref]
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. */