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work_on_cpu(): rewrite it to create a kernel thread on demand
Impact: circular locking bugfix The various implemetnations and proposed implemetnations of work_on_cpu() are vulnerable to various deadlocks because they all used queues of some form. Unrelated pieces of kernel code thus gained dependencies wherein if one work_on_cpu() caller holds a lock which some other work_on_cpu() callback also takes, the kernel could rarely deadlock. Fix this by creating a short-lived kernel thread for each work_on_cpu() invokation. This is not terribly fast, but the only current caller of work_on_cpu() is pci_call_probe(). It would be nice to find some other way of doing the node-local allocations in the PCI probe code so that we can zap work_on_cpu() altogether. The code there is rather nasty. I can't think of anything simple at this time... Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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@ -966,20 +966,20 @@ undo:
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}
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#ifdef CONFIG_SMP
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static struct workqueue_struct *work_on_cpu_wq __read_mostly;
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struct work_for_cpu {
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struct work_struct work;
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struct completion completion;
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long (*fn)(void *);
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void *arg;
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long ret;
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};
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static void do_work_for_cpu(struct work_struct *w)
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static int do_work_for_cpu(void *_wfc)
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{
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struct work_for_cpu *wfc = container_of(w, struct work_for_cpu, work);
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struct work_for_cpu *wfc = _wfc;
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wfc->ret = wfc->fn(wfc->arg);
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complete(&wfc->completion);
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return 0;
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}
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/**
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@ -990,17 +990,23 @@ static void do_work_for_cpu(struct work_struct *w)
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*
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* This will return the value @fn returns.
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* It is up to the caller to ensure that the cpu doesn't go offline.
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* The caller must not hold any locks which would prevent @fn from completing.
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*/
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long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
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{
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struct work_for_cpu wfc;
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INIT_WORK(&wfc.work, do_work_for_cpu);
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wfc.fn = fn;
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wfc.arg = arg;
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queue_work_on(cpu, work_on_cpu_wq, &wfc.work);
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flush_work(&wfc.work);
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struct task_struct *sub_thread;
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struct work_for_cpu wfc = {
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.completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
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.fn = fn,
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.arg = arg,
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};
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sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
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if (IS_ERR(sub_thread))
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return PTR_ERR(sub_thread);
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kthread_bind(sub_thread, cpu);
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wake_up_process(sub_thread);
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wait_for_completion(&wfc.completion);
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return wfc.ret;
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}
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EXPORT_SYMBOL_GPL(work_on_cpu);
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@ -1016,8 +1022,4 @@ void __init init_workqueues(void)
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hotcpu_notifier(workqueue_cpu_callback, 0);
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keventd_wq = create_workqueue("events");
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BUG_ON(!keventd_wq);
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#ifdef CONFIG_SMP
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work_on_cpu_wq = create_workqueue("work_on_cpu");
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BUG_ON(!work_on_cpu_wq);
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#endif
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}
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