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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2018-12-11 12:12:38 +0100
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-01-25 15:36:42 -0800
commite81baf4cb19a9b428ba477fd0423f81672a58817 (patch)
treefd518df0bf3f31968c4541ff488f0c727cc1b2b2 /kernel/rcu/srcutree.c
parentc8ca1aa774b20f182733d1661f3b6aa3105338e7 (diff)
downloadlinux-e81baf4cb19a9b428ba477fd0423f81672a58817.tar.bz2
srcu: Remove srcu_queue_delayed_work_on()
srcu_queue_delayed_work_on() disables preemption (and therefore CPU hotplug in RCU's case) and then checks based on its own accounting if a CPU is online. If the CPU is online it uses queue_delayed_work_on() otherwise it fallbacks to queue_delayed_work(). The problem here is that queue_work() on -RT does not work with disabled preemption. queue_work_on() works also on an offlined CPU. queue_delayed_work_on() has the problem that it is possible to program a timer on an offlined CPU. This timer will fire once the CPU is online again. But until then, the timer remains programmed and nothing will happen. Add a local timer which will fire (as requested per delay) on the local CPU and then enqueue the work on the specific CPU. RCUtorture testing with SRCU-P for 24h showed no problems. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu/srcutree.c')
-rw-r--r--kernel/rcu/srcutree.c55
1 files changed, 24 insertions, 31 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 3600d88d8956..7f041f2435df 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -58,6 +58,7 @@ static bool __read_mostly srcu_init_done;
static void srcu_invoke_callbacks(struct work_struct *work);
static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay);
static void process_srcu(struct work_struct *work);
+static void srcu_delay_timer(struct timer_list *t);
/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */
#define spin_lock_rcu_node(p) \
@@ -156,7 +157,8 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static)
snp->grphi = cpu;
}
sdp->cpu = cpu;
- INIT_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks);
+ INIT_WORK(&sdp->work, srcu_invoke_callbacks);
+ timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
sdp->ssp = ssp;
sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
if (is_static)
@@ -386,13 +388,19 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
} else {
flush_delayed_work(&ssp->work);
}
- for_each_possible_cpu(cpu)
+ for_each_possible_cpu(cpu) {
+ struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
+
if (quiesced) {
- if (WARN_ON(delayed_work_pending(&per_cpu_ptr(ssp->sda, cpu)->work)))
+ if (WARN_ON(timer_pending(&sdp->delay_work)))
+ return; /* Just leak it! */
+ if (WARN_ON(work_pending(&sdp->work)))
return; /* Just leak it! */
} else {
- flush_delayed_work(&per_cpu_ptr(ssp->sda, cpu)->work);
+ del_timer_sync(&sdp->delay_work);
+ flush_work(&sdp->work);
}
+ }
if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
WARN_ON(srcu_readers_active(ssp))) {
pr_info("%s: Active srcu_struct %p state: %d\n",
@@ -463,39 +471,23 @@ static void srcu_gp_start(struct srcu_struct *ssp)
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)
+static void srcu_delay_timer(struct timer_list *t)
{
- WRITE_ONCE(per_cpu(srcu_online, cpu), true);
-}
+ struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work);
-void srcu_offline_cpu(unsigned int cpu)
-{
- WRITE_ONCE(per_cpu(srcu_online, cpu), false);
+ queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
}
-/*
- * Place the workqueue handler on the specified CPU if online, otherwise
- * just run it whereever. This is useful for placing workqueue handlers
- * that are to invoke the specified CPU's callbacks.
- */
-static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
- struct delayed_work *dwork,
+static void srcu_queue_delayed_work_on(struct srcu_data *sdp,
unsigned long delay)
{
- bool ret;
+ if (!delay) {
+ queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work);
+ return;
+ }
- preempt_disable();
- if (READ_ONCE(per_cpu(srcu_online, cpu)))
- ret = queue_delayed_work_on(cpu, wq, dwork, delay);
- else
- ret = queue_delayed_work(wq, dwork, delay);
- preempt_enable();
- return ret;
+ timer_reduce(&sdp->delay_work, jiffies + delay);
}
/*
@@ -504,7 +496,7 @@ 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, rcu_gp_wq, &sdp->work, delay);
+ srcu_queue_delayed_work_on(sdp, delay);
}
/*
@@ -1186,7 +1178,8 @@ static void srcu_invoke_callbacks(struct work_struct *work)
struct srcu_data *sdp;
struct srcu_struct *ssp;
- sdp = container_of(work, struct srcu_data, work.work);
+ sdp = container_of(work, struct srcu_data, work);
+
ssp = sdp->ssp;
rcu_cblist_init(&ready_cbs);
spin_lock_irq_rcu_node(sdp);