On 07/29, Kirill A. Shutemov wrote: > > On Tue, Jul 28, 2015 at 02:35:04PM -0700, Andrew Morton wrote: > > On Tue, 28 Jul 2015 10:15:00 -0700 Kees Cook <keesc...@chromium.org> wrote: > > > > > From: Ricky Zhou <ric...@chromium.org> > > > > > > Checking mm_users > 1 does not mean a process is multithreaded. For > > > example, reading /proc/PID/maps temporarily increments mm_users, allowing > > > other processes to (accidentally) interfere with unshare() calls. > > > > > > This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly > > > returning EINVAL if another processes happened to be simultaneously > > > reading the maps file. > > > > Yikes. current_is_single_threaded() is expensive. Are we sure this > > isn't going to kill someone's workload? > > It's expensive only if mm_users > 1. We will go to for_each_process() only > if somebody outside of the process grabs mm_users references (like reading > /proc/PID/maps).
Yes, > Or if it called it from multithreaded application. Not really, please note the "negative fast-path" check: if (atomic_read(&task->signal->live) != 1) return false; > Acked-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> Same here, I think the patch is fine. I don't think that sys_setns() is performance critical, and Eric seems to agree with this change too. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/