On 2012/11/29 2:41, 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. Yes, we have the same point of view with you. We handle this problem in the ACPI based hot-plug framework as following: 1) hot add / hot remove complete successfully if no error happens; 2) automatic rollback to the original state if meets some error ; 3) rollback to the original if hot-plug operation cancelled by user ; > >> 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. Good idea ! we also implement a hot-plug operation in 3 phases: 1) acpihp_drv_pre_execute 2) acpihp_drv_execute 3) acpihp_drv_post_execute you may refer to : https://lkml.org/lkml/2012/11/4/79 > > 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. Yes, we have done this in acpihp_drv_pre_execute, and check following things: 1) Hot-plugble or not. the instance kernel memory you mentioned is also checked when memory device remove; 2) Dependency check involved. For instance, if hot-add a memory device, processor should be added first, otherwise it's not valid to this operation. 3) Race condition check. if the device and its dependent device is in hot-plug process, another request will be denied. No rollback is needed for the above checks. > > 2. Execute phase - Perform hot-add / hot-remove operation that can be > rolled-back in case of error or cancel. In this phase, we introduce a state machine for the hot-plugble device, please refer to: https://lkml.org/lkml/2012/11/4/79 I think we have the same idea for the major framework, but the ACPI based hot-plug framework implement it differently in detail, right ? Thanks Hanjun > > 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. > > > 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
