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From: Logan Gunthorpe <>
To: Vinod Koul <>
	Dan Williams <>
Subject: Re: [PATCH 1/5] dmaengine: Store module owner in dma_device struct
Date: Thu, 14 Nov 2019 10:03:05 -0700	[thread overview]
Message-ID: <> (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.


  reply	other threads:[~2019-11-14 17:03 UTC|newest]

Thread overview: 27+ 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
2019-12-16 19:01 [PATCH 0/5] Support hot-unbind in IOAT Logan Gunthorpe
2019-12-16 19:01 ` [PATCH 1/5] dmaengine: Store module owner in dma_device struct Logan Gunthorpe

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