On Monday, February 04, 2013 09:19:09 AM Toshi Kani wrote: > On Mon, 2013-02-04 at 15:21 +0100, Rafael J. Wysocki wrote: > > On Monday, February 04, 2013 04:48:10 AM Greg KH wrote: > > > On Sun, Feb 03, 2013 at 09:44:39PM +0100, Rafael J. Wysocki wrote: > > > > > Yes, but those are just remove events and we can only see how destructive they > > > > > were after the removal. The point is to be able to figure out whether or not > > > > > we *want* to do the removal in the first place. > > > > > > > > > > Say you have a computing node which signals a hardware problem in a processor > > > > > package (the container with CPU cores, memory, PCI host bridge etc.). You > > > > > may want to eject that package, but you don't want to kill the system this > > > > > way. So if the eject is doable, it is very much desirable to do it, but if it > > > > > is not doable, you'd rather shut the box down and do the replacement afterward. > > > > > That may be costly, however (maybe weeks of computations), so it should be > > > > > avoided if possible, but not at the expense of crashing the box if the eject > > > > > doesn't work out. > > > > > > > > It seems to me that we could handle that with the help of a new flag, say > > > > "no_eject", in struct device, a global mutex, and a function that will walk > > > > the given subtree of the device hierarchy and check if "no_eject" is set for > > > > any devices in there. Plus a global "no_eject" switch, perhaps. > > > > > > I think this will always be racy, or at worst, slow things down on > > > normal device operations as you will always be having to grab this flag > > > whenever you want to do something new. > > > > I don't see why this particular scheme should be racy, at least I don't see any > > obvious races in it (although I'm not that good at races detection in general, > > admittedly). > > > > Also, I don't expect that flag to be used for everything, just for things known > > to seriously break if forcible eject is done. That may be not precise enough, > > so that's a matter of defining its purpose more precisely. > > > > We can do something like that on the ACPI level (ie. introduce a no_eject flag > > in struct acpi_device and provide an iterface for the layers above ACPI to > > manipulate it) but then devices without ACPI namespace objects won't be > > covered. That may not be a big deal, though. > > I am afraid that bringing the device status management into the ACPI > level would not a good idea. acpi_device should only reflect ACPI > device object information, not how its actual device is being used. > > I like your initiative of acpi_scan_driver and I think scanning / > trimming of ACPI object info is what the ACPI drivers should do. ACPI drivers, yes, but the users of ACPI already rely on information in struct acpi_device. Like ACPI device power states, for example. So platform_no_eject(dev) is not much different in that respect from platform_pci_set_power_state(pci_dev). The whole "eject" concept is somewhat ACPI-specific, though, and the eject notifications come from ACPI, so I don't have a problem with limiting it to ACPI-backed devices for the time being. If it turns out the be useful outside of ACPI, then we can move it up to the driver core. For now I don't see a compelling reason to do that. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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>