On Thu, 2012-11-29 at 21:25 +0100, Rafael J. Wysocki wrote: > On Thursday, November 29, 2012 10:56:30 AM Toshi Kani wrote: > > On Thu, 2012-11-29 at 12:30 +0100, Vasilis Liaskovitis wrote: > > > On Thu, Nov 29, 2012 at 11:03:05AM +0100, Rafael J. Wysocki wrote: > > > > On Wednesday, November 28, 2012 06:15:42 PM Toshi Kani wrote: > > > > > On Wed, 2012-11-28 at 18:02 -0700, Toshi Kani wrote: > > > > > > On Thu, 2012-11-29 at 00:49 +0100, Rafael J. Wysocki wrote: > > > > > > > On Wednesday, November 28, 2012 02:02:48 PM Toshi Kani wrote: > > > > > > > > > > > > > > > Consider the following case: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > We hotremove the memory device by SCI and unbind it from the driver at the same time: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > CPUa CPUb > > > > > > > > > > > > > > > acpi_memory_device_notify() > > > > > > > > > > > > > > > unbind it from the driver > > > > > > > > > > > > > > > acpi_bus_hot_remove_device() > > > > > > > > > > > > > > > > > [...] > > > > Well, in the meantime I've had a look at acpi_bus_hot_remove_device() and > > > > friends and I think there's a way to address all of these problems > > > > without big redesign (for now). > > > > > > > > First, why don't we introduce an ACPI device flag (in the flags field of > > > > struct acpi_device) called eject_forbidden or something like this such that: > > > > > > > > (1) It will be clear by default. > > > > (2) It may only be set by a driver's .add() routine if necessary. > > > > (3) Once set, it may only be cleared by the driver's .remove() routine if > > > > it's safe to physically remove the device after the .remove(). > > > > > > > > Then, after the .remove() (which must be successful) has returned, and the > > > > flag is set, it will tell acpi_bus_remove() to return a specific error code > > > > (such as -EBUSY or -EAGAIN). It doesn't matter if .remove() was called > > > > earlier, because if it left the flag set, there's no way to clear it afterward > > > > and acpi_bus_remove() will see it set anyway. I think the struct acpi_device > > > > should be unregistered anyway if that error code is to be returned. > > > > > > > > [By the way, do you know where we free the memory allocated for struct > > > > acpi_device objects?] > > > > > > > > Now if acpi_bus_trim() gets that error code from acpi_bus_remove(), it should > > > > store it, but continue the trimming normally and finally it should return that > > > > error code to acpi_bus_hot_remove_device(). > > > > > > Side-note: In the pre_remove patches, acpi_bus_trim actually returns on the > > > first error from acpi_bus_remove (e.g. when memory offlining in pre_remove > > > fails). Trimming is not continued. > > > > > > Normally, acpi_bus_trim keeps trimming as you say, and always returns the last > > > error. Is this the desired behaviour that we want to keep for bus_trim? (This is > > > more a general question, not specific to the eject_forbidden suggestion) > > > > Your change makes sense to me. At least until we have rollback code in > > place, we need to fail as soon as we hit an error. > > Are you sure this makes sense? What happens to the devices that we have > trimmed already and then there's an error? Looks like they are just unusable > going forward, aren't they? Yes, the devices trimmed already are released from the kernel, and their memory ranges become unusable. This is bad. But I do not think we should trim further to make more devices unusable after an error. > > > > Now, if acpi_bus_hot_remove_device() gets that error code, it should just > > > > reverse the whole trimming (i.e. trigger acpi_bus_scan() from the device > > > > we attempted to eject) and notify the firmware about the failure. > > > > > > sounds like this rollback needs to be implemented in any solution we choose > > > to implement, correct? > > > > Yes, rollback is necessary. But I do not think we need to include it > > into your patch, though. > > As the first step, we should just trim everything and then return an error > code in my opinion. But we cannot trim devices with kernel memory. Thanks, -Toshi -- 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>