diff options
Diffstat (limited to 'debian/patches-rt/0161-srcu-use-cpu_online-instead-custom-check.patch')
| -rw-r--r-- | debian/patches-rt/0161-srcu-use-cpu_online-instead-custom-check.patch | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/debian/patches-rt/0161-srcu-use-cpu_online-instead-custom-check.patch b/debian/patches-rt/0161-srcu-use-cpu_online-instead-custom-check.patch new file mode 100644 index 000000000..626188f7a --- /dev/null +++ b/debian/patches-rt/0161-srcu-use-cpu_online-instead-custom-check.patch @@ -0,0 +1,96 @@ +From 4ce509b22af5e28f62c90f342169dad726731a39 Mon Sep 17 00:00:00 2001 +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Wed, 13 Sep 2017 14:43:41 +0200 +Subject: [PATCH 161/347] srcu: use cpu_online() instead custom check +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz + +The current check via srcu_online is slightly racy because after looking +at srcu_online there could be an interrupt that interrupted us long +enough until the CPU we checked against went offline. +An alternative would be to hold the hotplug rwsem (so the CPUs don't +change their state) and then check based on cpu_online() if we queue it +on a specific CPU or not. queue_work_on() itself can handle if something +is enqueued on an offline CPU but a timer which is enqueued on an offline +CPU won't fire until the CPU is back online. + +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/rcu/srcutree.c | 22 ++++------------------ + kernel/rcu/tree.c | 4 ---- + 2 files changed, 4 insertions(+), 22 deletions(-) + +diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c +index 1ff17e297f0c..df0375453ba1 100644 +--- a/kernel/rcu/srcutree.c ++++ b/kernel/rcu/srcutree.c +@@ -38,6 +38,7 @@ + #include <linux/delay.h> + #include <linux/module.h> + #include <linux/srcu.h> ++#include <linux/cpu.h> + + #include "rcu.h" + #include "rcu_segcblist.h" +@@ -460,21 +461,6 @@ static void srcu_gp_start(struct srcu_struct *sp) + WARN_ON_ONCE(state != SRCU_STATE_SCAN1); + } + +-/* +- * Track online CPUs to guide callback workqueue placement. +- */ +-DEFINE_PER_CPU(bool, srcu_online); +- +-void srcu_online_cpu(unsigned int cpu) +-{ +- WRITE_ONCE(per_cpu(srcu_online, cpu), true); +-} +- +-void srcu_offline_cpu(unsigned int cpu) +-{ +- WRITE_ONCE(per_cpu(srcu_online, cpu), false); +-} +- + /* + * Place the workqueue handler on the specified CPU if online, otherwise + * just run it whereever. This is useful for placing workqueue handlers +@@ -486,12 +472,12 @@ static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq, + { + bool ret; + +- preempt_disable(); +- if (READ_ONCE(per_cpu(srcu_online, cpu))) ++ cpus_read_lock(); ++ if (cpu_online(cpu)) + ret = queue_delayed_work_on(cpu, wq, dwork, delay); + else + ret = queue_delayed_work(wq, dwork, delay); +- preempt_enable(); ++ cpus_read_unlock(); + return ret; + } + +diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c +index ae716ca783bc..f162a4f54b05 100644 +--- a/kernel/rcu/tree.c ++++ b/kernel/rcu/tree.c +@@ -3784,8 +3784,6 @@ int rcutree_online_cpu(unsigned int cpu) + rnp->ffmask |= rdp->grpmask; + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } +- if (IS_ENABLED(CONFIG_TREE_SRCU)) +- srcu_online_cpu(cpu); + if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) + return 0; /* Too early in boot for scheduler work. */ + sync_sched_exp_online_cleanup(cpu); +@@ -3813,8 +3811,6 @@ int rcutree_offline_cpu(unsigned int cpu) + } + + rcutree_affinity_setting(cpu, cpu); +- if (IS_ENABLED(CONFIG_TREE_SRCU)) +- srcu_offline_cpu(cpu); + return 0; + } + +-- +2.36.1 + |