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/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> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.