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: 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>
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@ -69,10 +69,11 @@ static inline void unregister_cpu_notifier(struct notifier_block *nb)
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#endif
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int cpu_up(unsigned int cpu);
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extern void cpu_hotplug_init(void);
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extern void cpu_maps_update_begin(void);
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extern void cpu_maps_update_done(void);
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#else
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#else /* CONFIG_SMP */
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static inline int register_cpu_notifier(struct notifier_block *nb)
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{
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@ -87,10 +88,16 @@ static inline void cpu_hotplug_init(void)
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{
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}
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static inline void cpu_maps_update_begin(void)
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{
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}
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static inline void cpu_maps_update_done(void)
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{
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}
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#endif /* CONFIG_SMP */
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extern struct sysdev_class cpu_sysdev_class;
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extern void cpu_maps_update_begin(void);
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extern void cpu_maps_update_done(void);
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#ifdef CONFIG_HOTPLUG_CPU
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/* Stop CPUs going up and down. */
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@ -214,6 +214,8 @@ static inline int notifier_to_errno(int ret)
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#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
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#define CPU_DYING 0x0008 /* CPU (unsigned)v not running any task,
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* not handling interrupts, soon dead */
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#define CPU_POST_DEAD 0x0009 /* CPU (unsigned)v dead, cpu_hotplug
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* lock is dropped */
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/* Used for CPU hotplug events occuring while tasks are frozen due to a suspend
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* operation in progress
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@ -285,6 +285,11 @@ out_allowed:
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set_cpus_allowed_ptr(current, &old_allowed);
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out_release:
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cpu_hotplug_done();
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if (!err) {
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if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
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hcpu) == NOTIFY_BAD)
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BUG();
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}
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return err;
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}
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@ -828,7 +828,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
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err = create_workqueue_thread(cwq, singlethread_cpu);
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start_workqueue_thread(cwq, -1);
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} else {
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get_online_cpus();
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cpu_maps_update_begin();
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spin_lock(&workqueue_lock);
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list_add(&wq->list, &workqueues);
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spin_unlock(&workqueue_lock);
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@ -840,7 +840,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
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err = create_workqueue_thread(cwq, cpu);
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start_workqueue_thread(cwq, cpu);
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}
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put_online_cpus();
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cpu_maps_update_done();
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}
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if (err) {
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@ -854,8 +854,8 @@ EXPORT_SYMBOL_GPL(__create_workqueue_key);
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static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
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{
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/*
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* Our caller is either destroy_workqueue() or CPU_DEAD,
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* get_online_cpus() protects cwq->thread.
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* Our caller is either destroy_workqueue() or CPU_POST_DEAD,
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* cpu_add_remove_lock protects cwq->thread.
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*/
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if (cwq->thread == NULL)
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return;
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@ -865,7 +865,7 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
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flush_cpu_workqueue(cwq);
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/*
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* If the caller is CPU_DEAD and cwq->worklist was not empty,
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* If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
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* a concurrent flush_workqueue() can insert a barrier after us.
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* However, in that case run_workqueue() won't return and check
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* kthread_should_stop() until it flushes all work_struct's.
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@ -889,14 +889,14 @@ void destroy_workqueue(struct workqueue_struct *wq)
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const cpumask_t *cpu_map = wq_cpu_map(wq);
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int cpu;
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get_online_cpus();
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cpu_maps_update_begin();
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spin_lock(&workqueue_lock);
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list_del(&wq->list);
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spin_unlock(&workqueue_lock);
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for_each_cpu_mask_nr(cpu, *cpu_map)
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cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
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put_online_cpus();
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cpu_maps_update_done();
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free_percpu(wq->cpu_wq);
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kfree(wq);
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@ -935,7 +935,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
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case CPU_UP_CANCELED:
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start_workqueue_thread(cwq, -1);
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case CPU_DEAD:
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case CPU_POST_DEAD:
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cleanup_workqueue_thread(cwq);
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break;
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}
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@ -943,7 +943,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
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switch (action) {
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case CPU_UP_CANCELED:
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case CPU_DEAD:
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case CPU_POST_DEAD:
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cpu_clear(cpu, cpu_populated_map);
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}
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