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linux/Documentation/ABI/obsolete/sysfs-firmware-acpi

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ACPI / scan: Drop support for force_remove /sys/firmware/acpi/hotplug/force_remove was presumably added to support auto offlining in the past. This is, however, inherently dangerous for some hotplugable resources like memory. The memory offlining fails when the memory is still in use and cannot be dropped or migrated. If we ignore the failure we are basically allowing for subtle memory corruption or a crash. We have actually noticed the later while hitting BUG() during the memory hotremove (remove_memory): ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, check_memblock_offlined_cb); if (ret) BUG(); it took us quite non-trivial time realize that the customer had force_remove enabled. Even if the BUG was removed here and we could propagate the error up the call chain it wouldn't help at all because then we would hit a crash or a memory corruption later and harder to debug. So force_remove is unfixable for the memory hotremove. We haven't checked other hotplugable resources to be prone to a similar problems. Remove the force_remove functionality because it is not fixable currently. Keep the sysfs file and report an error if somebody tries to enable it. Encourage users to report about the missing functionality and work with them with an alternative solution. Reviewed-by: Lee, Chun-Yi <jlee@suse.com> Signed-off-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2017-04-03 07:40:23 +00:00
What: /sys/firmware/acpi/hotplug/force_remove
Date: Mar 2017
Contact: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Description:
Since the force_remove is inherently broken and dangerous to
use for some hotplugable resources like memory (because ignoring
the offline failure might lead to memory corruption and crashes)
enabling this knob is not safe and thus unsupported.
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