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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 <prsood@codeaurora.org>
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Paul E. McKenney 2018-01-08 14:35:52 -08:00
parent 65963d2461
commit ad7c946b35
4 changed files with 11 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
kernel/rcu/rcu.h
View File

@ -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

8
kernel/rcu/srcutree.c
View File

@ -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);
}
/*

6
kernel/rcu/tree.c
View File

@ -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"

2
kernel/rcu/tree_exp.h
View File

@ -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. */