On Tue, Mar 27, 2018 at 06:10:09AM +0900, Tetsuo Handa wrote: > On 2018/03/27 4:21, Cyrill Gorcunov wrote: > > That said I think using read-lock here would be a bug. > > If I understand correctly, the caller can't set both fields atomically, for > prctl() does not receive both fields at one call. > > prctl(PR_SET_MM, PR_SET_MM_ARG_START xor PR_SET_MM_ARG_END xor PR_SET_MM_ENV_START xor PR_SET_MM_ENV_END, new value, 0, 0); > True, but the key moment is that two/three/four system calls can run simultaneously. And while previously they are ordered by "write", with read lock they are completely unordered and this is really worries me. To be fair I would prefer to drop this old per-field interface completely. This per-field interface was rather an ugly solution from my side. > Then, I wonder whether reading arg_start|end and env_start|end atomically makes > sense. Just retry reading if arg_start > env_end or env_start > env_end is fine? Tetsuo, let me re-read this code tomorrow, maybe I miss something obvious.
