dpkg fails on sparc64 (was: [PATCH v4 4/7] mm/thp: Carry over dirty bit when thp splits on pmd)

[Anatoly Pugachev <matorola@gmail.com>]

On Thu, Aug 11, 2022 at 12:13:28PM -0400, Peter Xu wrote:
> Carry over the dirty bit from pmd to pte when a huge pmd splits.  It
> shouldn't be a correctness issue since when pmd_dirty() we'll have the page
> marked dirty anyway, however having dirty bit carried over helps the next
> initial writes of split ptes on some archs like x86.
> 
> Reviewed-by: Huang Ying <ying.huang@intel.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  mm/huge_memory.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)


Hello!

Tried to update my debian sparc64 sid (unstable) linux distro to latest
version of available packages, got dpkg segfault... 

$ apt update -y
...
Unpacking linux-image-sparc64-smp (6.0.2-1) ...
E: Sub-process /usr/bin/dpkg received a segmentation fault.

Downgraded dpkg from 1.21.9 to 1.21.8 / 1.21.7 (2-3 monthes old
versions) - still getting segfault on package install (which was never
an issue before, even on this old dpkg versions).

Tried to gdb backtrace core file, which is unlucky :


root@ttip:/# apt install -y linux-image-sparc64-smp ccache qemu-utils xdelta qemu-system-x86 distcc qemu-efi-aarch64 pkg-kde-tools
...
Preparing to unpack .../2-linux-image-6.0.0-1-sparc64-smp_6.0.2-1_sparc64.deb ...
Unpacking linux-image-6.0.0-1-sparc64-smp (6.0.2-1) ...
Selecting previously unselected package linux-image-sparc64-smp.
Preparing to unpack .../3-linux-image-sparc64-smp_6.0.2-1_sparc64.deb ...
Unpacking linux-image-sparc64-smp (6.0.2-1) ...
E: Sub-process /usr/bin/dpkg received a segmentation fault.
root@ttip:/# ls -l core.4751
-rw------- 1 root root 25042944 Oct 21 14:38 core.4751
root@ttip:/# gdb -q -c core.4751
GNU gdb (Debian 12.1-4) 12.1
[New LWP 4751]
Core was generated by `/usr/bin/dpkg --status-fd 15 --no-triggers --unpack --auto-deconfigure --recurs'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0xfff800010089cde4 in ?? ()
(gdb) bt
#0  0xfff800010089cde4 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
(gdb)


rebooted from my compiled kernel 6.1.0-rc1 to older (debian) kernel -
5.19.0-2-sparc64-smp

dpkg installed packages without any problems. Removed just installed
packages, rebooted to 6.1.0-rc1 and tried to install packages, dpkg got
segfault again.

Recompiled 6.1.0-rc1 with gcc-11 instead of gcc-12, still segfaults...
... bisect time ...

mator@ttip:~/linux-2.6$ git bisect log
# bad: [9abf2313adc1ca1b6180c508c25f22f9395cc780] Linux 6.1-rc1
# good: [4fe89d07dcc2804c8b562f6c7896a45643d34b2f] Linux 6.0
git bisect start 'v6.1-rc1' 'v6.0'
# good: [18fd049731e67651009f316195da9281b756f2cf] Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
git bisect good 18fd049731e67651009f316195da9281b756f2cf
# good: [4c540c92b46497dcda59203eea78e4620bc96f47] RISC-V: Add mvendorid, marchid, and mimpid to /proc/cpuinfo output
git bisect good 4c540c92b46497dcda59203eea78e4620bc96f47
# bad: [27bc50fc90647bbf7b734c3fc306a5e61350da53] Merge tag 'mm-stable-2022-10-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
git bisect bad 27bc50fc90647bbf7b734c3fc306a5e61350da53
# good: [ada3bfb6492a6d0d3eca50f3b61315fe032efc72] Merge tag 'tpmdd-next-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd
git bisect good ada3bfb6492a6d0d3eca50f3b61315fe032efc72
# bad: [5f7fa13fa858c17580ed513bd5e0a4b36d68fdd6] mm: add pageblock_align() macro
git bisect bad 5f7fa13fa858c17580ed513bd5e0a4b36d68fdd6
# bad: [54a611b605901c7d5d05b6b8f5d04a6ceb0962aa] Maple Tree: add new data structure
git bisect bad 54a611b605901c7d5d05b6b8f5d04a6ceb0962aa
# good: [59298997df89e19aad426d4ae0a7e5037074da5a] x86/uaccess: avoid check_object_size() in copy_from_user_nmi()
git bisect good 59298997df89e19aad426d4ae0a7e5037074da5a
# good: [04c6b79ae4f0bcbd96afd7cea5e1a8848162438e] btrfs: convert __process_pages_contig() to use filemap_get_folios_contig()
git bisect good 04c6b79ae4f0bcbd96afd7cea5e1a8848162438e
# good: [da29499124cd2221539b235c1f93c7d93faf6565] mm, hwpoison: use __PageMovable() to detect non-lru movable pages
git bisect good da29499124cd2221539b235c1f93c7d93faf6565
# bad: [eed9a328aa1ae6ac1edaa026957e6882f57de0dd] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG
git bisect bad eed9a328aa1ae6ac1edaa026957e6882f57de0dd
# bad: [f347c9d2697fcbbb64e077f7113a3887a181b8c0] filemap: make the accounting of thrashing more consistent
git bisect bad f347c9d2697fcbbb64e077f7113a3887a181b8c0
# good: [eba4d770efc86a3710e36b828190858abfa3bb74] mm/swap: comment all the ifdef in swapops.h
git bisect good eba4d770efc86a3710e36b828190858abfa3bb74
# bad: [2e3468778dbe3ec389a10c21a703bb8e5be5cfbc] mm: remember young/dirty bit for page migrations
git bisect bad 2e3468778dbe3ec389a10c21a703bb8e5be5cfbc
# bad: [0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb] mm/thp: carry over dirty bit when thp splits on pmd
git bisect bad 0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb
# good: [0d206b5d2e0d7d7f09ac9540e3ab3e35a34f536e] mm/swap: add swp_offset_pfn() to fetch PFN from swap entry
git bisect good 0d206b5d2e0d7d7f09ac9540e3ab3e35a34f536e
# first bad commit: [0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb] mm/thp: carry over dirty bit when thp splits on pmd


mator@ttip:~/linux-2.6$ git bisect good
0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb is the first bad commit
commit 0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb
Author: Peter Xu <peterx@redhat.com>
Date:   Thu Aug 11 12:13:28 2022 -0400

    mm/thp: carry over dirty bit when thp splits on pmd

    Carry over the dirty bit from pmd to pte when a huge pmd splits.  It
    shouldn't be a correctness issue since when pmd_dirty() we'll have the
    page marked dirty anyway, however having dirty bit carried over helps the
    next initial writes of split ptes on some archs like x86.

    Link: https://lkml.kernel.org/r/20220811161331.37055-5-peterx@redhat.com



So, v6.0-rc3-176-g0d206b5d2e0d) does not segfault dpkg,
v6.0-rc3-177-g0ccf7f168e17 segfaults it on package install.

dpkg test was (apt) install/remove some packages, segfaults only on install
(not remove).

Reverted 0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb from top of v6.1-rc1 and
tried to compile kernel, but got error 

mm/huge_memory.c: In function ‘__split_huge_pmd_locked’:
mm/huge_memory.c:2129:17: error: ‘dirty’ undeclared (first use in this function)
 2129 |                 dirty = is_migration_entry_dirty(entry);
      |                 ^~~~~
mm/huge_memory.c:2129:17: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [scripts/Makefile.build:250: mm/huge_memory.o] Error 1

So can't test v6.1-rc1 with patch reverted...