kernel: mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW

In the Linux kernel, the following vulnerability has been resolved: mm/gup: fix FOLLFORCE COW security issue and remove FOLLCOW Ever since the Dirty COW CVE-2016-5195 security issue happened, we know that FOLLFORCE can be possibly dangerous, especially if there are races that can be exploited by...