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Commit 6b44003e authored by Andrew Morton's avatar Andrew Morton Committed by Rusty Russell
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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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 1c99315b

kernel/workqueue.c

+19 −17
Original line number Diff line number Diff line
@@ -966,20 +966,20 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb, 
}



#ifdef CONFIG_SMP

static struct workqueue_struct *work_on_cpu_wq __read_mostly;



struct work_for_cpu {

	struct work_struct work;

	struct completion completion;

	long (*fn)(void *);

	void *arg;

	long ret;

};



static void do_work_for_cpu(struct work_struct *w)

static int do_work_for_cpu(void *_wfc)

{

	struct work_for_cpu *wfc = container_of(w, struct work_for_cpu, work);



	struct work_for_cpu *wfc = _wfc;

	wfc->ret = wfc->fn(wfc->arg);

	complete(&wfc->completion);

	return 0;

}



/**
@@ -990,17 +990,23 @@ static void do_work_for_cpu(struct work_struct *w) 
 *

 * This will return the value @fn returns.

 * It is up to the caller to ensure that the cpu doesn't go offline.

 * The caller must not hold any locks which would prevent @fn from completing.

 */

long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)

{

	struct work_for_cpu wfc;



	INIT_WORK(&wfc.work, do_work_for_cpu);

	wfc.fn = fn;

	wfc.arg = arg;

	queue_work_on(cpu, work_on_cpu_wq, &wfc.work);

	flush_work(&wfc.work);

	struct task_struct *sub_thread;

	struct work_for_cpu wfc = {

		.completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),

		.fn = fn,

		.arg = arg,

	};



	sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");

	if (IS_ERR(sub_thread))

		return PTR_ERR(sub_thread);

	kthread_bind(sub_thread, cpu);

	wake_up_process(sub_thread);

	wait_for_completion(&wfc.completion);

	return wfc.ret;

}

EXPORT_SYMBOL_GPL(work_on_cpu);
@@ -1016,8 +1022,4 @@ void __init init_workqueues(void) 
	hotcpu_notifier(workqueue_cpu_callback, 0);

	keventd_wq = create_workqueue("events");

	BUG_ON(!keventd_wq);

#ifdef CONFIG_SMP

	work_on_cpu_wq = create_workqueue("work_on_cpu");

	BUG_ON(!work_on_cpu_wq);

#endif

}