On Wed, Nov 26, 2014 at 12:33:41PM -0800, Mandeep Sandhu wrote: > > While the kernel driver has no problem with hot-removal, I see that if I > > "unregister" our UIO driver in response to the removal, then the mapping > for > > the hardware's physical memory would become "invalid" (done by UIO on > > unregsiter). This could possibly cause the user-space process to crash > due to > > illegal memory access. > > You should just get 0xff on the memory reads, right? You can catch the > signal for invalid memory accesses. > > > Wouldn't I get an illegal memory access, as UIO would've removed the mappings > that it setup when I registered the UIO driver? I saw the userspace process > segfault after removal. I don't know, never tried it. What about catching the signal for this? > > Is there a "standard" way to handle this scenario, i.e for hotpluggable > > hardware using UIO? > > Your kernel driver knows when the device is removed, so have it tell > userspace this. Or, just tie into libudev and have your userspace > program be notified when the device goes away. > > > Right. This is what I'm trying to do using a udev "remove" rule. No, just have libudev tell you about the problem, don't create a whole new rule for this, that's overkill and messy and not dynamic at all. > Although the > question still remains, what will happen if the device is being actively > accessed _before_ the signal reaches the process. Is it safe to do > "uio_unregister_device" while a userspace process is accessing the device? I don't know, try it and see :) > I saw a patch for this very situation (UIO & hotplug) being discussed on LKML > almost 4 yrs back, although I don't see it in my kernel version - 3.16.0 > (Ubuntu 3.16.0-24-generic). > The LKML link: > > https://lkml.org/lkml/2010/9/20/21 > > Wouldn't this solve the issue? I wonder why it didn't make it into mainline? No idea, that UIO maintainer must be really lazy and never apply patches :) Try that series on your kernel and see what happens. If it works, please resend that patch series. thanks, greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
