Recently, I hit the following issue when running upstream.

  kernel BUG at mm/vmscan.c:1521!
  invalid opcode: 0000 [#1] SMP KASAN PTI
  CPU: 0 PID: 23385 Comm: syz-executor.6 Not tainted 5.4.0-rc4+ #1
  RIP: 0010:shrink_page_list+0x12b6/0x3530 mm/vmscan.c:1521
  Call Trace:
   reclaim_pages+0x499/0x800 mm/vmscan.c:2188
   madvise_cold_or_pageout_pte_range+0x58a/0x710 mm/madvise.c:453
   walk_pmd_range mm/pagewalk.c:53 [inline]
   walk_pud_range mm/pagewalk.c:112 [inline]
   walk_p4d_range mm/pagewalk.c:139 [inline]
   walk_pgd_range mm/pagewalk.c:166 [inline]
   __walk_page_range+0x45a/0xc20 mm/pagewalk.c:261
   walk_page_range+0x179/0x310 mm/pagewalk.c:349
   madvise_pageout_page_range mm/madvise.c:506 [inline]
   madvise_pageout+0x1f0/0x330 mm/madvise.c:542
   madvise_vma mm/madvise.c:931 [inline]
   __do_sys_madvise+0x7d2/0x1600 mm/madvise.c:1113
   do_syscall_64+0x9f/0x4c0 arch/x86/entry/common.c:290
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

madvise_pageout() accesses the specified range of the vma and isolates
them, then runs shrink_page_list() to reclaim its memory.  But it also
isolates the unevictable pages to reclaim.  Hence, we can catch the
cases in shrink_page_list().

The root cause is that we scan the page tables instead of specific LRU
list.  and so we need to filter out the unevictable lru pages from our
end.

Link: http://lkml.kernel.org/r/1572616245-18946-1-git-send-email-zhongjiang@huawei.com
Fixes: 1a4e58cc ("mm: introduce MADV_PAGEOUT")
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>