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commit1f503443e7upstream. After commitba72b4c8cf("mm/sparsemem: support sub-section hotplug"), when a mem section is fully deactivated, section_mem_map still records the section's start pfn, which is not used any more and will be reassigned during re-addition. In analogy with alloc/free pattern, it is better to clear all fields of section_mem_map. Beside this, it breaks the user space tool "makedumpfile" [1], which makes assumption that a hot-removed section has mem_map as NULL, instead of checking directly against SECTION_MARKED_PRESENT bit. (makedumpfile will be better to change the assumption, and need a patch) The bug can be reproduced on IBM POWERVM by "drmgr -c mem -r -q 5" , trigger a crash, and save vmcore by makedumpfile [1]: makedumpfile, commit e73016540293 ("[v1.6.7] Update version") Link: http://lkml.kernel.org/r/1579487594-28889-1-git-send-email-kernelfans@gmail.com Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Baoquan He <bhe@redhat.com> Cc: Qian Cai <cai@lca.pw> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.