From: Vinod Koul <vkoul@kernel.org>
To: Logan Gunthorpe <logang@deltatee.com>
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: Fri, 22 Nov 2019 10:50:10 +0530 [thread overview]
Message-ID: <20191122052010.GO82508@vkoul-mobl> (raw)
In-Reply-To: <fa45de06-089f-367c-7816-2ee040e41d24@deltatee.com>
On 14-11-19, 10:03, Logan Gunthorpe wrote:
>
>
> 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.
That sounds okay then.
>
> 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
--
~Vinod
next prev parent reply other threads:[~2019-11-22 5:20 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
2019-11-22 5:20 ` Vinod Koul [this message]
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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