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workqueues: make get_online_cpus() useable for work->func()

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workqueue_cpu_callback(CPU_DEAD) flushes cwq->thread under
cpu_maps_update_begin().  This means that the multithreaded workqueues
can't use get_online_cpus() due to the possible deadlock, very bad and
very old problem.

Introduce the new state, CPU_POST_DEAD, which is called after
cpu_hotplug_done() but before cpu_maps_update_done().

Change workqueue_cpu_callback() to use CPU_POST_DEAD instead of CPU_DEAD.
This means that create/destroy functions can't rely on get_online_cpus()
any longer and should take cpu_add_remove_lock instead.

[akpm@linux-foundation.org: fix CONFIG_SMP=n]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Gautham R Shenoy <ego@in.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-07-25 01:47:50 -07:00 committed by Linus Torvalds
parent 8616a89ab7
commit 3da1c84c00
4 changed files with 27 additions and 13 deletions
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15
include/linux/cpu.h
View file

@ -69,10 +69,11 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
#endif
int cpu_up(unsigned int cpu);
extern void cpu_hotplug_init(void);
extern void cpu_maps_update_begin(void);
extern void cpu_maps_update_done(void);
#else
#else /* CONFIG_SMP */
static inline int register_cpu_notifier(struct notifier_block *nb)
{
@ -87,10 +88,16 @@ static inline void cpu_hotplug_init(void)
{
}
static inline void cpu_maps_update_begin(void)
{
}
static inline void cpu_maps_update_done(void)
{
}
#endif /* CONFIG_SMP */
extern struct sysdev_class cpu_sysdev_class;
extern void cpu_maps_update_begin(void);
extern void cpu_maps_update_done(void);
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */

2
include/linux/notifier.h
View file

@ -214,6 +214,8 @@ static inline int notifier_to_errno(int ret)
#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
#define CPU_DYING 0x0008 /* CPU (unsigned)v not running any task,
* not handling interrupts, soon dead */
#define CPU_POST_DEAD 0x0009 /* CPU (unsigned)v dead, cpu_hotplug
* lock is dropped */
/* Used for CPU hotplug events occuring while tasks are frozen due to a suspend
* operation in progress

5
kernel/cpu.c
View file

@ -285,6 +285,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
set_cpus_allowed_ptr(current, &old_allowed);
out_release:
cpu_hotplug_done();
if (!err) {
if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
hcpu) == NOTIFY_BAD)
BUG();
}
return err;
}

18
kernel/workqueue.c
View file

@ -828,7 +828,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
err = create_workqueue_thread(cwq, singlethread_cpu);
start_workqueue_thread(cwq, -1);
} else {
get_online_cpus();
cpu_maps_update_begin();
spin_lock(&workqueue_lock);
list_add(&wq->list, &workqueues);
spin_unlock(&workqueue_lock);
@ -840,7 +840,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
err = create_workqueue_thread(cwq, cpu);
start_workqueue_thread(cwq, cpu);
}
put_online_cpus();
cpu_maps_update_done();
}
if (err) {
@ -854,8 +854,8 @@ EXPORT_SYMBOL_GPL(__create_workqueue_key);
static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
{
/*
* Our caller is either destroy_workqueue() or CPU_DEAD,
* get_online_cpus() protects cwq->thread.
* Our caller is either destroy_workqueue() or CPU_POST_DEAD,
* cpu_add_remove_lock protects cwq->thread.
*/
if (cwq->thread == NULL)
return;
@ -865,7 +865,7 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
flush_cpu_workqueue(cwq);
/*
* If the caller is CPU_DEAD and cwq->worklist was not empty,
* If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
* a concurrent flush_workqueue() can insert a barrier after us.
* However, in that case run_workqueue() won't return and check
* kthread_should_stop() until it flushes all work_struct's.
@ -889,14 +889,14 @@ void destroy_workqueue(struct workqueue_struct *wq)
const cpumask_t *cpu_map = wq_cpu_map(wq);
int cpu;
get_online_cpus();
cpu_maps_update_begin();
spin_lock(&workqueue_lock);
list_del(&wq->list);
spin_unlock(&workqueue_lock);
for_each_cpu_mask_nr(cpu, *cpu_map)
cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
put_online_cpus();
cpu_maps_update_done();
free_percpu(wq->cpu_wq);
kfree(wq);
@ -935,7 +935,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
case CPU_UP_CANCELED:
start_workqueue_thread(cwq, -1);
case CPU_DEAD:
case CPU_POST_DEAD:
cleanup_workqueue_thread(cwq);
break;
}
@ -943,7 +943,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
switch (action) {
case CPU_UP_CANCELED:
case CPU_DEAD:
case CPU_POST_DEAD:
cpu_clear(cpu, cpu_populated_map);
}