89 lines
2.7 KiB
Diff
89 lines
2.7 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 13 Sep 2017 14:43:41 +0200
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Subject: [PATCH] srcu: use cpu_online() instead custom check
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz
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The current check via srcu_online is slightly racy because after looking
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at srcu_online there could be an interrupt that interrupted us long
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enough until the CPU we checked against went offline.
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An alternative would be to hold the hotplug rwsem (so the CPUs don't
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change their state) and then check based on cpu_online() if we queue it
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on a specific CPU or not. queue_work_on() itself can handle if something
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is enqueued on an offline CPU but a timer which is enqueued on an offline
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CPU won't fire until the CPU is back online.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/rcu/srcutree.c | 22 ++++------------------
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kernel/rcu/tree.c | 4 ----
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2 files changed, 4 insertions(+), 22 deletions(-)
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--- a/kernel/rcu/srcutree.c
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+++ b/kernel/rcu/srcutree.c
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@@ -38,6 +38,7 @@
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/srcu.h>
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+#include <linux/cpu.h>
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#include "rcu.h"
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#include "rcu_segcblist.h"
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@@ -459,21 +460,6 @@ static void srcu_gp_start(struct srcu_st
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}
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/*
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- * Track online CPUs to guide callback workqueue placement.
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- */
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-DEFINE_PER_CPU(bool, srcu_online);
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-
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-void srcu_online_cpu(unsigned int cpu)
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-{
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- WRITE_ONCE(per_cpu(srcu_online, cpu), true);
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-}
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-
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-void srcu_offline_cpu(unsigned int cpu)
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-{
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- WRITE_ONCE(per_cpu(srcu_online, cpu), false);
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-}
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-
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-/*
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* Place the workqueue handler on the specified CPU if online, otherwise
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* just run it whereever. This is useful for placing workqueue handlers
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* that are to invoke the specified CPU's callbacks.
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@@ -484,12 +470,12 @@ static bool srcu_queue_delayed_work_on(i
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{
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bool ret;
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- preempt_disable();
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- if (READ_ONCE(per_cpu(srcu_online, cpu)))
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+ cpus_read_lock();
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+ if (cpu_online(cpu))
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ret = queue_delayed_work_on(cpu, wq, dwork, delay);
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else
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ret = queue_delayed_work(wq, dwork, delay);
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- preempt_enable();
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+ cpus_read_unlock();
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return ret;
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}
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--- a/kernel/rcu/tree.c
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+++ b/kernel/rcu/tree.c
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@@ -3767,8 +3767,6 @@ int rcutree_online_cpu(unsigned int cpu)
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rnp->ffmask |= rdp->grpmask;
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raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
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}
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- if (IS_ENABLED(CONFIG_TREE_SRCU))
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- srcu_online_cpu(cpu);
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if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
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return 0; /* Too early in boot for scheduler work. */
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sync_sched_exp_online_cleanup(cpu);
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@@ -3796,8 +3794,6 @@ int rcutree_offline_cpu(unsigned int cpu
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}
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rcutree_affinity_setting(cpu, cpu);
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- if (IS_ENABLED(CONFIG_TREE_SRCU))
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- srcu_offline_cpu(cpu);
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return 0;
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}
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