cpu-hotplug: replace per-subsystem mutexes with get_online_cpus()
This patch converts the known per-subsystem mutexes to get_online_cpus
put_online_cpus. It also eliminates the CPU_LOCK_ACQUIRE and
CPU_LOCK_RELEASE hotplug notification events.
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 0c40cc0..5dfbc68 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -207,9 +207,7 @@
#define CPU_DOWN_PREPARE 0x0005 /* CPU (unsigned)v going down */
#define CPU_DOWN_FAILED 0x0006 /* CPU (unsigned)v NOT going down */
#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
-#define CPU_LOCK_ACQUIRE 0x0008 /* Acquire all hotcpu locks */
-#define CPU_LOCK_RELEASE 0x0009 /* Release all hotcpu locks */
-#define CPU_DYING 0x000A /* CPU (unsigned)v not running any task,
+#define CPU_DYING 0x0008 /* CPU (unsigned)v not running any task,
* not handling interrupts, soon dead */
/* Used for CPU hotplug events occuring while tasks are frozen due to a suspend
diff --git a/kernel/cpu.c b/kernel/cpu.c
index b0c4152..e0d3a4f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -218,7 +218,6 @@
return -EINVAL;
cpu_hotplug_begin();
- raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
hcpu, -1, &nr_calls);
if (err == NOTIFY_BAD) {
@@ -271,7 +270,6 @@
out_allowed:
set_cpus_allowed(current, old_allowed);
out_release:
- raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
cpu_hotplug_done();
return err;
}
@@ -302,7 +300,6 @@
return -EINVAL;
cpu_hotplug_begin();
- raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
-1, &nr_calls);
if (ret == NOTIFY_BAD) {
@@ -326,7 +323,6 @@
if (ret != 0)
__raw_notifier_call_chain(&cpu_chain,
CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
- raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
cpu_hotplug_done();
return ret;
diff --git a/kernel/sched.c b/kernel/sched.c
index 672aa68..c0e2db6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -439,7 +439,6 @@
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
-static DEFINE_MUTEX(sched_hotcpu_mutex);
static inline void check_preempt_curr(struct rq *rq, struct task_struct *p)
{
@@ -4546,13 +4545,13 @@
struct task_struct *p;
int retval;
- mutex_lock(&sched_hotcpu_mutex);
+ get_online_cpus();
read_lock(&tasklist_lock);
p = find_process_by_pid(pid);
if (!p) {
read_unlock(&tasklist_lock);
- mutex_unlock(&sched_hotcpu_mutex);
+ put_online_cpus();
return -ESRCH;
}
@@ -4592,7 +4591,7 @@
}
out_unlock:
put_task_struct(p);
- mutex_unlock(&sched_hotcpu_mutex);
+ put_online_cpus();
return retval;
}
@@ -4649,7 +4648,7 @@
struct task_struct *p;
int retval;
- mutex_lock(&sched_hotcpu_mutex);
+ get_online_cpus();
read_lock(&tasklist_lock);
retval = -ESRCH;
@@ -4665,7 +4664,7 @@
out_unlock:
read_unlock(&tasklist_lock);
- mutex_unlock(&sched_hotcpu_mutex);
+ put_online_cpus();
return retval;
}
@@ -5625,9 +5624,6 @@
struct rq *rq;
switch (action) {
- case CPU_LOCK_ACQUIRE:
- mutex_lock(&sched_hotcpu_mutex);
- break;
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
@@ -5697,9 +5693,6 @@
spin_unlock_irq(&rq->lock);
break;
#endif
- case CPU_LOCK_RELEASE:
- mutex_unlock(&sched_hotcpu_mutex);
- break;
}
return NOTIFY_OK;
}
@@ -6655,10 +6648,10 @@
{
int err;
- mutex_lock(&sched_hotcpu_mutex);
+ get_online_cpus();
detach_destroy_domains(&cpu_online_map);
err = arch_init_sched_domains(&cpu_online_map);
- mutex_unlock(&sched_hotcpu_mutex);
+ put_online_cpus();
return err;
}
@@ -6769,12 +6762,12 @@
{
cpumask_t non_isolated_cpus;
- mutex_lock(&sched_hotcpu_mutex);
+ get_online_cpus();
arch_init_sched_domains(&cpu_online_map);
cpus_andnot(non_isolated_cpus, cpu_possible_map, cpu_isolated_map);
if (cpus_empty(non_isolated_cpus))
cpu_set(smp_processor_id(), non_isolated_cpus);
- mutex_unlock(&sched_hotcpu_mutex);
+ put_online_cpus();
/* XXX: Theoretical race here - CPU may be hotplugged now */
hotcpu_notifier(update_sched_domains, 0);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 8db0b59..52db48e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -67,9 +67,8 @@
#endif
};
-/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
- threads to each one as cpus come/go. */
-static DEFINE_MUTEX(workqueue_mutex);
+/* Serializes the accesses to the list of workqueues. */
+static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static int singlethread_cpu __read_mostly;
@@ -592,8 +591,6 @@
* Returns zero on success.
* Returns -ve errno on failure.
*
- * Appears to be racy against CPU hotplug.
- *
* schedule_on_each_cpu() is very slow.
*/
int schedule_on_each_cpu(work_func_t func)
@@ -605,7 +602,7 @@
if (!works)
return -ENOMEM;
- preempt_disable(); /* CPU hotplug */
+ get_online_cpus();
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);
@@ -613,8 +610,8 @@
set_bit(WORK_STRUCT_PENDING, work_data_bits(work));
__queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), work);
}
- preempt_enable();
flush_workqueue(keventd_wq);
+ put_online_cpus();
free_percpu(works);
return 0;
}
@@ -750,8 +747,10 @@
err = create_workqueue_thread(cwq, singlethread_cpu);
start_workqueue_thread(cwq, -1);
} else {
- mutex_lock(&workqueue_mutex);
+ get_online_cpus();
+ spin_lock(&workqueue_lock);
list_add(&wq->list, &workqueues);
+ spin_unlock(&workqueue_lock);
for_each_possible_cpu(cpu) {
cwq = init_cpu_workqueue(wq, cpu);
@@ -760,7 +759,7 @@
err = create_workqueue_thread(cwq, cpu);
start_workqueue_thread(cwq, cpu);
}
- mutex_unlock(&workqueue_mutex);
+ put_online_cpus();
}
if (err) {
@@ -775,7 +774,7 @@
{
/*
* Our caller is either destroy_workqueue() or CPU_DEAD,
- * workqueue_mutex protects cwq->thread
+ * get_online_cpus() protects cwq->thread.
*/
if (cwq->thread == NULL)
return;
@@ -810,9 +809,11 @@
struct cpu_workqueue_struct *cwq;
int cpu;
- mutex_lock(&workqueue_mutex);
+ get_online_cpus();
+ spin_lock(&workqueue_lock);
list_del(&wq->list);
- mutex_unlock(&workqueue_mutex);
+ spin_unlock(&workqueue_lock);
+ put_online_cpus();
for_each_cpu_mask(cpu, *cpu_map) {
cwq = per_cpu_ptr(wq->cpu_wq, cpu);
@@ -835,13 +836,6 @@
action &= ~CPU_TASKS_FROZEN;
switch (action) {
- case CPU_LOCK_ACQUIRE:
- mutex_lock(&workqueue_mutex);
- return NOTIFY_OK;
-
- case CPU_LOCK_RELEASE:
- mutex_unlock(&workqueue_mutex);
- return NOTIFY_OK;
case CPU_UP_PREPARE:
cpu_set(cpu, cpu_populated_map);
@@ -854,7 +848,8 @@
case CPU_UP_PREPARE:
if (!create_workqueue_thread(cwq, cpu))
break;
- printk(KERN_ERR "workqueue for %i failed\n", cpu);
+ printk(KERN_ERR "workqueue [%s] for %i failed\n",
+ wq->name, cpu);
return NOTIFY_BAD;
case CPU_ONLINE:
diff --git a/mm/slab.c b/mm/slab.c
index ff31261..40c00da 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -730,8 +730,7 @@
#endif
/*
- * 1. Guard access to the cache-chain.
- * 2. Protect sanity of cpu_online_map against cpu hotplug events
+ * Guard access to the cache-chain.
*/
static DEFINE_MUTEX(cache_chain_mutex);
static struct list_head cache_chain;
@@ -1331,12 +1330,11 @@
int err = 0;
switch (action) {
- case CPU_LOCK_ACQUIRE:
- mutex_lock(&cache_chain_mutex);
- break;
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
+ mutex_lock(&cache_chain_mutex);
err = cpuup_prepare(cpu);
+ mutex_unlock(&cache_chain_mutex);
break;
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
@@ -1373,9 +1371,8 @@
#endif
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
+ mutex_lock(&cache_chain_mutex);
cpuup_canceled(cpu);
- break;
- case CPU_LOCK_RELEASE:
mutex_unlock(&cache_chain_mutex);
break;
}
@@ -2170,6 +2167,7 @@
* We use cache_chain_mutex to ensure a consistent view of
* cpu_online_map as well. Please see cpuup_callback
*/
+ get_online_cpus();
mutex_lock(&cache_chain_mutex);
list_for_each_entry(pc, &cache_chain, next) {
@@ -2396,6 +2394,7 @@
panic("kmem_cache_create(): failed to create slab `%s'\n",
name);
mutex_unlock(&cache_chain_mutex);
+ put_online_cpus();
return cachep;
}
EXPORT_SYMBOL(kmem_cache_create);
@@ -2547,9 +2546,11 @@
int ret;
BUG_ON(!cachep || in_interrupt());
+ get_online_cpus();
mutex_lock(&cache_chain_mutex);
ret = __cache_shrink(cachep);
mutex_unlock(&cache_chain_mutex);
+ put_online_cpus();
return ret;
}
EXPORT_SYMBOL(kmem_cache_shrink);
@@ -2575,6 +2576,7 @@
BUG_ON(!cachep || in_interrupt());
/* Find the cache in the chain of caches. */
+ get_online_cpus();
mutex_lock(&cache_chain_mutex);
/*
* the chain is never empty, cache_cache is never destroyed
@@ -2584,6 +2586,7 @@
slab_error(cachep, "Can't free all objects");
list_add(&cachep->next, &cache_chain);
mutex_unlock(&cache_chain_mutex);
+ put_online_cpus();
return;
}
@@ -2592,6 +2595,7 @@
__kmem_cache_destroy(cachep);
mutex_unlock(&cache_chain_mutex);
+ put_online_cpus();
}
EXPORT_SYMBOL(kmem_cache_destroy);
