On Fri, 5 Feb 2016 12:23:13 -0800 John Stultz <john.stu...@linaro.org> wrote:
> On Fri, Feb 5, 2016 at 12:13 PM, Andrew Morton > <a...@linux-foundation.org> wrote: > > On Fri, 5 Feb 2016 10:08:43 -0800 John Stultz <john.stu...@linaro.org> > > wrote: > >> @@ -2218,6 +2222,27 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, > >> arg2, unsigned long, arg3, > >> case PR_GET_TID_ADDRESS: > >> error = prctl_get_tid_address(me, (int __user **)arg2); > >> break; > >> + case PR_SET_TIMERSLACK_PID: > >> + rcu_read_lock(); > >> + tsk = find_task_by_vpid((pid_t)arg3); > > > > hm, as far as I can tell this is the first instance in which prctl() is > > used to play with a task other than "current". Maybe this isn't a good > > precedent. > > > > If you look at all the other diddle-other-task functions in > > kernel/sys.c, you'll see that they are standalone syscalls. What > > you've done here is just a bit lazy: added what is effectively a new > > standalone syscall, only it has been hidden within the prctl() switch > > statement. > > > > I don't see a practical problem with this - we could have implemented > > all those other syscalls as prctl submodes as well. But we didn't... > > > > IOW, it would be more consistent to add sys_set_timer_slack()? > > I'm fine with moving this way. > > Ruchi/Rom: Any objections to that idea? > > Thomas/Arjan: Any other functionality we should consider including > when adding a syscall to tweak timer slack? A syscall is quite a bit more fuss - implement it on x86_64, provide a no-op default in sys_ni.c, add a test suite into tools/testing/selftests (mainly for arch maintainers), wait for the various arch maintainers to wire it up. Fortunately the build system now emits little messages which tell maintainers that there's a new syscall which needs looking at. And a manpage will be needed, but a prctl manpage patch would have been needed anyway.
