On Thu, Nov 29, 2012 at 12:05:20AM +0100, Rafael J. Wysocki wrote: > On Wednesday, November 28, 2012 02:46:33 PM Greg KH wrote: > > > So, it looks like the driver core wants us to handle driver unbinding no > > > matter what. > > > > Yes. Well, the driver core does the unbinding no matter what, if it was > > told, by a user, to do so. Why is that a problem? The user then is > > responsible for any bad things (i.e. not able to control the device any > > more), if they do so. > > I don't really agree with that, because the user may simply not know what > the consequences of that will be. In my not so humble opinion any interface > allowing user space to crash the kernel is a bad one. And this is an example > of that. This has been in place since 2005, over 7 years now, and I have never heard any problems with it being used to crash the kernel, despite the easy ability for people to unbind all of their devices from drivers and instantly cause a system hang. So really doubt this is a problem in real life :) > > > This pretty much means that it is a bad idea to have a driver that is > > > exposed as a "device driver" in sysfs for memory hotplugging. > > > > Again, why? All this means is that the driver is now not connected to > > the device (memory in this case.) The memory is still there, still > > operates as before, only difference is, the driver can't touch it > > anymore. > > > > This is the same for any ACPI driver, and has been for years. > > Except that if this driver has been unbound and the removal is triggered by > an SCI, the core will just go on and remove the memory, although it may > be killing the kernel this way. Why would memory go away if a driver is unbound from a device? The device didn't go away. It's the same if the driver was a module and it was unloaded, you should not turn memory off in that situation, right? Are you also going to prevent module unloading of this driver? > Arguably, this may be considered as the core's fault, but the only way to > fix that would be to move the code from that driver into the core and not to > register it as a "driver" any more. Which was my point. :-) No, I think people are totally overreacting to the unbind/bind files, which are there to aid in development, and in adding new device ids to drivers, as well as sometimes doing a hacky revoke() call. > > Please don't confuse unbind with any "normal" system operation, it is > > not to be used for memory hotplug, or anything else like this. > > > > Also, if you really do not want to do this, turn off the ability to > > unbind/bind for these devices, that is under your control in your bus > > logic. > > OK, but how? I'm looking at driver_unbind() and not seeing any way to do > that actually. See the suppress_bind_attrs field in struct device_driver. It's even documented in device.h, but sadly, no one reads documentation :) I recommend you set this field if you don't want the bind/unbind files to show up for your memory driver, although I would argue that the driver needs to be fixed up to not do foolish things like removing memory from a system unless it really does go away... hope this helps, greg k-h -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>