linux-kernel - Re: [PATCH v9 7/8] PCI/P2PDMA: Allow userspace VMA allocations through sysfs

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Date:   Thu, 1 Sep 2022 12:14:25 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v9 7/8] PCI/P2PDMA: Allow userspace VMA allocations
 through sysfs




On 2022-09-01 10:42, Greg Kroah-Hartman wrote:
> On Thu, Sep 01, 2022 at 10:32:55AM -0600, Logan Gunthorpe wrote:
>> On 2022-09-01 10:20, Greg Kroah-Hartman wrote:
>>> On Thu, Aug 25, 2022 at 09:24:24AM -0600, Logan Gunthorpe wrote:
>>>> +	/*
>>>> +	 * Removing the alloc attribute from sysfs will call
>>>> +	 * unmap_mapping_range() on the inode, teardown any existing userspace
>>>> +	 * mappings and prevent new ones from being created.
>>>> +	 */
>>>> +	sysfs_remove_file_from_group(&pdev->dev.kobj, &p2pmem_alloc_attr.attr,
>>>> +				     p2pmem_group.name);
>>>
>>> Wait, why are you manually removing the sysfs file here?  It's part of
>>> the group, if you do this then it is gone for forever, right?  Why
>>> manually do this the sysfs core should handle this for you if the device
>>> is removed.
>>
>> We have to make sure the mappings are all removed before the cleanup of
>> devm_memremap_pages() which will wait for all the pages to be freed.
> 
> Then don't use devm_ functions.  Why not just use the manual functions
> instead as you know when you want to tear this down.

Well we haven't plugged in a remove call into p2pdma, that would be more
work and more interfaces touching the PCI code. Note: this code isn't a
driver but a set of PCI helpers available to other PCI drivers.
Everything that's setup is using the devm interfaces and gets torn down
with the same. So I don't really see the benefit of making the change
you propose.

Logan