On Tue, Jul 28, 2015 at 02:35:04PM -0700, Andrew Morton wrote: > On Tue, 28 Jul 2015 10:15:00 -0700 Kees Cook <[email protected]> wrote: > > > From: Ricky Zhou <[email protected]> > > > > 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). Or if it called it from multithreaded application. Acked-by: Kirill A. Shutemov <[email protected]> -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
