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Commit 3da1c84c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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



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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarGautham 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8616a89a

include/linux/cpu.h

+11 −4
Original line number Diff line number Diff line
@@ -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. */

include/linux/notifier.h

+2 −0
Original line number Diff line number Diff line
@@ -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

kernel/cpu.c

+5 −0
Original line number Diff line number Diff line
@@ -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;

}

kernel/workqueue.c

+9 −9
Original line number Diff line number Diff line
@@ -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);

	}