Post #3969054

Fun Linux fact: On a Linux system where /tmp/ is tmpfs, if you create the following directories: /tmp/pathwalktest/tmp/pathwalktest/a/tmp/pathwalktest/a/b/tmp/pathwalktest/c and call rename("/tmp/pathwalktest/a/b", "/tmp/pathwalktest/b") then a concurrent open("/tmp/pathwalktest/a/b/../c", O_RDONLY) normally won't end up opening /tmp/pathwalktest/c. But a concurrent open("/proc/self/root/tmp/pathwalktest/a/b/../c", O_RDONLY) can end up doing that with a simple ABA race ordering. (This is all working as intended, this is just a difference between rcu-walk and ref-walk; going through procfs magiclinks forces ref-walk mode.)