On Fri, 2012-12-07 at 00:00 +0800, Jiang Liu wrote: > On 11/29/2012 02:41 AM, Toshi Kani wrote: > > On Wed, 2012-11-28 at 19:05 +0800, Hanjun Guo wrote: > >> On 2012/11/24 1:50, Vasilis Liaskovitis wrote: > >>> As discussed in https://patchwork.kernel.org/patch/1581581/ > >>> the driver core remove function needs to always succeed. This means we need > >>> to know that the device can be successfully removed before acpi_bus_trim / > >>> acpi_bus_hot_remove_device are called. This can cause panics when OSPM-initiated > >>> or SCI-initiated eject of memory devices fail e.g with: > >>> echo 1 >/sys/bus/pci/devices/PNP0C80:XX/eject > >>> > >>> since the ACPI core goes ahead and ejects the device regardless of whether the > >>> the memory is still in use or not. > >>> > >>> For this reason a new acpi_device operation called prepare_remove is introduced. > >>> This operation should be registered for acpi devices whose removal (from kernel > >>> perspective) can fail. Memory devices fall in this category. > >>> > >>> acpi_bus_remove() is changed to handle removal in 2 steps: > >>> - preparation for removal i.e. perform part of removal that can fail. Should > >>> succeed for device and all its children. > >>> - if above step was successfull, proceed to actual device removal > >> > >> Hi Vasilis, > >> We met the same problem when we doing computer node hotplug, It is a good idea > >> to introduce prepare_remove before actual device removal. > >> > >> I think we could do more in prepare_remove, such as rollback. In most cases, we can > >> offline most of memory sections except kernel used pages now, should we rollback > >> and online the memory sections when prepare_remove failed ? > > > > I think hot-plug operation should have all-or-nothing semantics. That > > is, an operation should either complete successfully, or rollback to the > > original state. > > > >> As you may know, the ACPI based hotplug framework we are working on already addressed > >> this problem, and the way we slove this problem is a bit like yours. > >> > >> We introduce hp_ops in struct acpi_device_ops: > >> struct acpi_device_ops { > >> acpi_op_add add; > >> acpi_op_remove remove; > >> acpi_op_start start; > >> acpi_op_bind bind; > >> acpi_op_unbind unbind; > >> acpi_op_notify notify; > >> #ifdef CONFIG_ACPI_HOTPLUG > >> struct acpihp_dev_ops *hp_ops; > >> #endif /* CONFIG_ACPI_HOTPLUG */ > >> }; > >> > >> in hp_ops, we divide the prepare_remove into six small steps, that is: > >> 1) pre_release(): optional step to mark device going to be removed/busy > >> 2) release(): reclaim device from running system > >> 3) post_release(): rollback if cancelled by user or error happened > >> 4) pre_unconfigure(): optional step to solve possible dependency issue > >> 5) unconfigure(): remove devices from running system > >> 6) post_unconfigure(): free resources used by devices > >> > >> In this way, we can easily rollback if error happens. > >> How do you think of this solution, any suggestion ? I think we can achieve > >> a better way for sharing ideas. :) > > > > Yes, sharing idea is good. :) I do not know if we need all 6 steps (I > > have not looked at all your changes yet..), but in my mind, a hot-plug > > operation should be composed with the following 3 phases. > > > > 1. Validate phase - Verify if the request is a supported operation. All > > known restrictions are verified at this phase. For instance, if a > > hot-remove request involves kernel memory, it is failed in this phase. > > Since this phase makes no change, no rollback is necessary to fail. > > > > 2. Execute phase - Perform hot-add / hot-remove operation that can be > > rolled-back in case of error or cancel. > > > > 3. Commit phase - Perform the final hot-add / hot-remove operation that > > cannot be rolled-back. No error / cancel is allowed in this phase. For > > instance, eject operation is performed at this phase. > Hi Toshi, > There are one more step needed. Linux provides sysfs interfaces to > online/offline CPU/memory sections, so we need to protect from concurrent > operations from those interfaces when doing physical hotplug. Think about > following sequence: > Thread 1 > 1. validate conditions for hot-removal > 2. offline memory section A > 3. online memory section A > 4. offline memory section B > 5 hot-remove memory device hosting A and B. Hi Gerry, I agree. And I am working on a proposal that tries to address this issue by integrating both sysfs and hotplug operations into a framework. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
