From ad7c946b35ad455417fdd4bc0e17deda4011841b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 8 Jan 2018 14:35:52 -0800 Subject: [PATCH] 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. Note that this moves SRCU from system_power_efficient_wq to a normal workqueue. In the unlikely event that this results in measurable degradation, a separate power-efficient workqueue will be creates for SRCU. Reported-by: Prateek Sood Reported-by: Tejun Heo Signed-off-by: Paul E. McKenney Acked-by: Tejun Heo --- kernel/rcu/rcu.h | 1 + kernel/rcu/srcutree.c | 8 +++----- kernel/rcu/tree.c | 6 ++++++ kernel/rcu/tree_exp.h | 2 +- 4 files changed, 11 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 1c868bc..7a693e3 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -485,6 +485,7 @@ 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_wq; #endif /* #else #ifdef CONFIG_TINY_RCU */ #ifdef CONFIG_RCU_NOCB_CPU diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 045b559b..743d183 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -492,8 +492,7 @@ 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, - &sdp->work, delay); + srcu_queue_delayed_work_on(sdp->cpu, rcu_gp_wq, &sdp->work, delay); } /* @@ -691,8 +690,7 @@ 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, - srcu_get_delay(sp)); + queue_delayed_work(rcu_gp_wq, &sp->work, srcu_get_delay(sp)); } spin_unlock_irqrestore_rcu_node(sp, flags); } @@ -1225,7 +1223,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) spin_unlock_irq_rcu_node(sp); if (pushgp) - queue_delayed_work(system_power_efficient_wq, &sp->work, delay); + queue_delayed_work(rcu_gp_wq, &sp->work, delay); } /* diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 99d404c..2a73469 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4167,6 +4167,8 @@ static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp) pr_cont("\n"); } +struct workqueue_struct *rcu_gp_wq; + void __init rcu_init(void) { int cpu; @@ -4193,6 +4195,10 @@ void __init rcu_init(void) rcu_cpu_starting(cpu); rcutree_online_cpu(cpu); } + + /* Create workqueue for expedited GPs and for Tree SRCU. */ + rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0); + WARN_ON(!rcu_gp_wq); } #include "tree_exp.h" diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 6ad8764..f72eefa 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -626,7 +626,7 @@ 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_wq, &rew.rew_work); } /* Wait for expedited grace period to complete. */ -- 2.7.4