Messages in this thread | | | Date | Fri, 5 Feb 2016 12:13:53 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread. |
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On Fri, 5 Feb 2016 10:08:43 -0800 John Stultz <john.stultz@linaro.org> wrote:
> From: Ruchi Kandoi <kandoiruchi@google.com> > > This allows power/performance management software to set timer > slack for other threads according to its policy for the thread > (such as when the thread is designated foreground vs. background > activity) > > Second argument is similar to PR_SET_TIMERSLACK, if non-zero > then the slack is set to that value otherwise sets it to the > default for the thread. > > Takes PID of the thread as the third argument. > > This interface checks that the calling task has permissions to > to use PTRACE_MODE_ATTACH on the target task, so that we can > ensure arbitrary apps do not change the timer slack for other > apps. > > Additional fixes from Ruchi and Micha Kalfon <micha@cellrox.com> > have been folded into this patch to make it easier to reivew. > > ... > > @@ -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()?
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