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Message-ID: <20150626021522.GA5714@redhat.com>
Date: Fri, 26 Jun 2015 04:15:22 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>, paulmck@...ux.vnet.ibm.com,
tj@...nel.org, mingo@...hat.com, der.herr@...r.at,
dave@...olabs.net, riel@...hat.com, viro@...IV.linux.org.uk,
torvalds@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org
Subject: [RFC PATCH 5/6] stop_machine: change stop_two_cpus() just use
stop_cpu(), kill lg_double_lock/unlock
Now that stop_cpus() is not "exclusive" if cpumask's don't overlap, we
can turn stop_two_cpus() into a trivial wrapper on top of stop_cpus().
Note: if zalloc_cpumask_var(cpumask, GFP_KERNEL) is not an option, we
can reimplement this function using stop_work_{alloc,free}_one().
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
include/linux/lglock.h | 5 ---
kernel/locking/lglock.c | 22 ----------------
kernel/stop_machine.c | 64 ++++++++--------------------------------------
3 files changed, 11 insertions(+), 80 deletions(-)
diff --git a/include/linux/lglock.h b/include/linux/lglock.h
index c92ebd1..0081f00 100644
--- a/include/linux/lglock.h
+++ b/include/linux/lglock.h
@@ -52,15 +52,10 @@ struct lglock {
static struct lglock name = { .lock = &name ## _lock }
void lg_lock_init(struct lglock *lg, char *name);
-
void lg_local_lock(struct lglock *lg);
void lg_local_unlock(struct lglock *lg);
void lg_local_lock_cpu(struct lglock *lg, int cpu);
void lg_local_unlock_cpu(struct lglock *lg, int cpu);
-
-void lg_double_lock(struct lglock *lg, int cpu1, int cpu2);
-void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2);
-
void lg_global_lock(struct lglock *lg);
void lg_global_unlock(struct lglock *lg);
diff --git a/kernel/locking/lglock.c b/kernel/locking/lglock.c
index 951cfcd..86ae2ae 100644
--- a/kernel/locking/lglock.c
+++ b/kernel/locking/lglock.c
@@ -60,28 +60,6 @@ void lg_local_unlock_cpu(struct lglock *lg, int cpu)
}
EXPORT_SYMBOL(lg_local_unlock_cpu);
-void lg_double_lock(struct lglock *lg, int cpu1, int cpu2)
-{
- BUG_ON(cpu1 == cpu2);
-
- /* lock in cpu order, just like lg_global_lock */
- if (cpu2 < cpu1)
- swap(cpu1, cpu2);
-
- preempt_disable();
- lock_acquire_shared(&lg->lock_dep_map, 0, 0, NULL, _RET_IP_);
- arch_spin_lock(per_cpu_ptr(lg->lock, cpu1));
- arch_spin_lock(per_cpu_ptr(lg->lock, cpu2));
-}
-
-void lg_double_unlock(struct lglock *lg, int cpu1, int cpu2)
-{
- lock_release(&lg->lock_dep_map, 1, _RET_IP_);
- arch_spin_unlock(per_cpu_ptr(lg->lock, cpu1));
- arch_spin_unlock(per_cpu_ptr(lg->lock, cpu2));
- preempt_enable();
-}
-
void lg_global_lock(struct lglock *lg)
{
int i;
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 4b23875..572abc9 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -20,7 +20,6 @@
#include <linux/kallsyms.h>
#include <linux/smpboot.h>
#include <linux/atomic.h>
-#include <linux/lglock.h>
/*
* Structure to determine completion condition and record errors. May
@@ -97,14 +96,6 @@ static bool stop_work_alloc(const struct cpumask *cpumask, bool wait)
return true;
}
-/*
- * Avoids a race between stop_two_cpus and global stop_cpus, where
- * the stoppers could get queued up in reverse order, leading to
- * system deadlock. Using an lglock means stop_two_cpus remains
- * relatively cheap.
- */
-DEFINE_STATIC_LGLOCK(stop_cpus_lock);
-
static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
{
memset(done, 0, sizeof(*done));
@@ -276,50 +267,17 @@ static int multi_cpu_stop(void *data)
*/
int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
{
- struct cpu_stop_done done;
- struct cpu_stop_work work1, work2;
- struct multi_stop_data msdata;
-
- preempt_disable();
- msdata = (struct multi_stop_data){
- .fn = fn,
- .data = arg,
- .num_threads = 2,
- .active_cpus = cpumask_of(cpu1),
- };
-
- work1 = work2 = (struct cpu_stop_work){
- .fn = multi_cpu_stop,
- .arg = &msdata,
- .done = &done
- };
-
- cpu_stop_init_done(&done, 2);
- set_state(&msdata, MULTI_STOP_PREPARE);
-
- /*
- * If we observe both CPUs active we know _cpu_down() cannot yet have
- * queued its stop_machine works and therefore ours will get executed
- * first. Or its not either one of our CPUs that's getting unplugged,
- * in which case we don't care.
- *
- * This relies on the stopper workqueues to be FIFO.
- */
- if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
- preempt_enable();
- return -ENOENT;
- }
-
- lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
- cpu_stop_queue_work(cpu1, &work1);
- cpu_stop_queue_work(cpu2, &work2);
- lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
-
- preempt_enable();
+ cpumask_var_t cpumask;
+ int ret;
- wait_for_completion(&done.completion);
+ if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
+ return -ENOMEM;
- return done.executed ? done.ret : -ENOENT;
+ cpumask_set_cpu(cpu1, cpumask);
+ cpumask_set_cpu(cpu2, cpumask);
+ ret = stop_cpus(cpumask, fn, arg);
+ free_cpumask_var(cpumask);
+ return ret;
}
/**
@@ -355,7 +313,7 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
* preempted by a stopper which might wait for other stoppers
* to enter @fn which can lead to deadlock.
*/
- lg_global_lock(&stop_cpus_lock);
+ preempt_disable();
for_each_cpu(cpu, cpumask) {
work = &per_cpu(cpu_stopper.stop_work, cpu);
work->fn = fn;
@@ -363,7 +321,7 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
work->done = done;
cpu_stop_queue_work(cpu, work);
}
- lg_global_unlock(&stop_cpus_lock);
+ preempt_enable();
}
static int __stop_cpus(const struct cpumask *cpumask,
--
1.5.5.1
--
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