On Thu, 2012-11-29 at 21:30 +0100, Rafael J. Wysocki wrote: > On Thursday, November 29, 2012 10:03:12 AM Toshi Kani wrote: > > On Thu, 2012-11-29 at 11:15 +0100, Rafael J. Wysocki wrote: > > > On Wednesday, November 28, 2012 11:41:36 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. > > > > > > That's correct. > > > > > > > > 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. > > > > > > Actually, we can't do it this way, because the conditions may change between > > > the check and the execution. So the first phase needs to involve execution > > > to some extent, although only as far as it remains reversible. > > > > For memory hot-remove, we can check if the target memory ranges are > > within ZONE_MOVABLE. We should not allow user to change this setup > > during hot-remove operation. Other things may be to check if a target > > node contains cpu0 (until it is supported), the console UART (assuming > > we cannot delete it), etc. We should avoid doing rollback as much as we > > can. > > Yes, we can make some checks upfront as an optimization and fail early if > the conditions are not met, but for correctness we need to repeat those > checks later anyway. Once we've decided to go for the eject, the conditions > must hold whatever happens. Agreed. 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
