Description: mm, oom: fix concurrent munlock and oom reaper unmap
References:
 https://marc.info/?l=linux-kernel&m=152400522806945
 http://www.openwall.com/lists/oss-security/2018/04/24/3
 https://marc.info/?l=linux-kernel&m=152460926619256
 https://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git/commit/?h=auto-latest&id=8392ca77d55d2d2cb0d5546c1ff920f7334f0306
Notes:
 carnil> Introduced in 212925802454672e6cd2949a727f5e2c1377bf06 (4.14-rc1)
 carnil> proposed fix: https://marc.info/?l=linux-kernel&m=152460926619256
Bugs:
upstream: released (4.17-rc5) [27ae357fa82be5ab73b2ef8d39dcb8ca2563483a]
4.9-upstream-stable: N/A "Vulnerable code not present"
3.16-upstream-stable: N/A "Vulnerable code not present"
3.2-upstream-stable: N/A "Vulnerable code not present"
sid: released (4.16.12-1)
4.9-stretch-security: N/A "Vulnerable code not present"
3.16-jessie-security: N/A "Vulnerable code not present"
3.2-wheezy-security: N/A "Vulnerable code not present"