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
