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
