dmaengine Archive on lore.kernel.org
 help / color / Atom feed
From: Logan Gunthorpe <logang@deltatee.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH 1/5] dmaengine: Store module owner in dma_device struct
Date: Thu, 14 Nov 2019 10:03:05 -0700
Message-ID: <fa45de06-089f-367c-7816-2ee040e41d24@deltatee.com> (raw)
In-Reply-To: <20191114045555.GJ952516@vkoul-mobl>



On 2019-11-13 9:55 p.m., Vinod Koul wrote:
>> But that's the problem. We can't expect our users to be "nice" and not
>> unbind when the driver is in use. Killing the kernel if the user
>> unexpectedly unbinds is not acceptable.
> 
> And that is why we review the code and ensure this does not happen and
> behaviour is as expected

Yes, but the current code can kill the kernel when the driver is unbound.

>>>> I suspect this is less of an issue for most devices as they wouldn't
>>>> normally be unbound while in use (for example there's really no reason
>>>> to ever unbind IOAT seeing it's built into the system). Though, the fact
>>>> is, the user could unbind these devices at anytime and we don't want to
>>>> panic if they do.
>>>
>>> There are many drivers which do modules so yes I am expecting unbind and
>>> even a bind following that to work
>>
>> Except they will panic if they unbind while in use, so that's a
>> questionable definition of "work".
> 
> dmaengine core has module reference so while they are being used they
> won't be removed (unless I complete misread the driver core behaviour)

Yes, as I mentioned in my other email, holding a module reference does
not prevent the driver from being unbound. Any driver can be unbound by
the user at any time without the module being removed.

Essentially, at any time, a user can do this:

echo 0000:83:00.4 > /sys/bus/pci/drivers/plx_dma/unbind

Which will call plx_dma_remove() regardless of whether anyone has a
reference to the module, and regardless of whether the dma channel is
currently in use. I feel it is important that drivers support this
without crashing, and my plx_dma driver does the correct thing here.

Logan


  reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-22 21:46 [PATCH 0/5] PLX Switch DMA Engine Driver Logan Gunthorpe
2019-10-22 21:46 ` [PATCH 1/5] dmaengine: Store module owner in dma_device struct Logan Gunthorpe
2019-11-09 17:18   ` Vinod Koul
2019-11-11 16:50     ` Logan Gunthorpe
2019-11-12  5:56       ` Vinod Koul
2019-11-12 16:45         ` Logan Gunthorpe
2019-11-14  4:55           ` Vinod Koul
2019-11-14 17:03             ` Logan Gunthorpe [this message]
2019-11-22  5:20               ` Vinod Koul
2019-11-22 16:53                 ` Dave Jiang
2019-11-22 20:50                   ` Dan Williams
2019-11-22 20:56                     ` Logan Gunthorpe
2019-11-22 21:01                       ` Dan Williams
2019-11-22 21:42                         ` Dave Jiang
2019-12-10  9:53                           ` Vinod Koul
2019-12-10 17:39                             ` Logan Gunthorpe
2019-10-22 21:46 ` [PATCH 2/5] dmaengine: Call module_put() after device_free_chan_resources() Logan Gunthorpe
2019-10-22 21:46 ` [PATCH 3/5] dmaengine: plx-dma: Introduce PLX DMA engine PCI driver skeleton Logan Gunthorpe
2019-11-09 17:35   ` Vinod Koul
2019-11-11 17:50     ` Logan Gunthorpe
2019-11-12  6:09       ` Vinod Koul
2019-11-12 17:22         ` Logan Gunthorpe
2019-10-22 21:46 ` [PATCH 4/5] dmaengine: plx-dma: Implement hardware initialization and cleanup Logan Gunthorpe
2019-10-22 21:46 ` [PATCH 5/5] dmaengine: plx-dma: Implement descriptor submission Logan Gunthorpe
2019-11-09 17:40   ` Vinod Koul
2019-11-11 18:11     ` Logan Gunthorpe

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=fa45de06-089f-367c-7816-2ee040e41d24@deltatee.com \
    --to=logang@deltatee.com \
    --cc=dan.j.williams@intel.com \
    --cc=dmaengine@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=vkoul@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

dmaengine Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/dmaengine/0 dmaengine/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dmaengine dmaengine/ https://lore.kernel.org/dmaengine \
		dmaengine@vger.kernel.org
	public-inbox-index dmaengine

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.dmaengine


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git