linux-kernel - Re: [PATCH v7 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem stats

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Message-ID: <834b26a8-545c-98e0-fd95-231b701abae6@deltatee.com>
Date:   Tue, 25 Sep 2018 12:51:09 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Bart Van Assche <bvanassche@....org>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-block@...r.kernel.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v7 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem
 stats



On 2018-09-25 12:31 p.m., Bart Van Assche wrote:
> On Tue, 2018-09-25 at 12:15 -0600, Logan Gunthorpe wrote:
>> On 2018-09-25 11:29 a.m., Bart Van Assche wrote:
>>> On Tue, 2018-09-25 at 10:22 -0600, Logan Gunthorpe wrote:
>>>> @@ -83,9 +132,14 @@ static int pci_p2pdma_setup(struct pci_dev *pdev)
>>>>  
>>>>  	pdev->p2pdma = p2p;
>>>>  
>>>> +	error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
>>>> +	if (error)
>>>> +		goto out_pool_destroy;
>>>> +
>>>>  	return 0;
>>>>  
>>>>  out_pool_destroy:
>>>> +	pdev->p2pdma = NULL;
>>>>  	gen_pool_destroy(p2p->pool);
>>>>  out:
>>>>  	devm_kfree(&pdev->dev, p2p);
>>>
>>> This doesn't look right to me. Shouldn't devm_remove_action() be called instead
>>> of devm_kfree() if sysfs_create_group() fails?
>>
>> That makes no sense to me. We are reversing a devm_kzalloc() not a
>> custom action....
> 
> In case what I wrote was not clear: both devm_kzalloc() and
> devm_add_action_or_reset() have to be reversed if sysfs_create_group() fails.
> devm_add_action_or_reset() calls devres_add(). The latter function adds an
> element to the dev->devres_head list. So I think that only calling devm_kfree()
> if sysfs_create_group() fails will lead to corruption of the dev->devres_head
> list.

I don't see how it would corrupt the list. devres_remove() uses
list_del_init() which doesn't require that you only remove the tail from
the list... The way I read the code, you can remove any devm action at
any time.

Logan