linux-kernel - Re: [patch] bdi: add a user-tunable cpu

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Date:	Mon, 03 Dec 2012 10:49:25 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Zach Brown <zab@...hat.com>
Cc:	Jens Axboe <jaxboe@...ionio.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] bdi: add a user-tunable cpu_list for the bdi flusher threads

Zach Brown <zab@...hat.com> writes:

>> +	ret = cpulist_parse(buf, newmask);
>> +	if (!ret) {
>> +		spin_lock(&bdi->wb_lock);
>> +		task = wb->task;
>> +		get_task_struct(task);
>> +		spin_unlock(&bdi->wb_lock);
>> +		if (task)
>> +			ret = set_cpus_allowed_ptr(task, newmask);
>> +		put_task_struct(task);
>
> If that test for a non-null task is needed then surely the get and put
> need to be similarly protected :).

How embarrassing.

>> +		bdi->flusher_cpumask = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
>> +		if (!bdi->flusher_cpumask)
>> +			return -ENOMEM;
>
> The bare GFP_KERNEL raises an eyebrow.  Some bdi_init() callers like
> blk_alloc_queue_node() look like they'll want to pass in a gfp_t for the
> allocation.

I'd be surprised if that was necessary, seeing how every single caller
of blk_alloc_queue_node passes in GFP_KERNEL.  I'll make the change,
though, there aren't too many callers of bdi_init out there.

> And shouldn't this be freed in the error path of bdi_init()?

Yes.  ;-)

Thanks!
Jeff
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