prctl: adds PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread.

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 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)

Change-Id: I744d451ff4e60dae69f38f53948ff36c51c14a3f
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>

Conflicts:
	include/linux/prctl.h
	kernel/sys.c

1 files changed, 19 insertions, 0 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 1c69aa7..8d1142a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -40,6 +40,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/version.h>
 #include <linux/ctype.h>
+#include <linux/sched.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -1660,6 +1661,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		unsigned long, arg4, unsigned long, arg5)
 {
 	struct task_struct *me = current;
+	struct task_struct *tsk;
 	unsigned char comm[sizeof(me->comm)];
 	long error;
 
@@ -1804,6 +1806,23 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			else
 				error = PR_MCE_KILL_DEFAULT;
 			break;
+		case PR_SET_TIMERSLACK_PID:
+			rcu_read_lock();
+			tsk = find_task_by_pid_ns((pid_t)arg3, &init_pid_ns);
+			if (tsk == NULL) {
+				rcu_read_unlock();
+				return -EINVAL;
+			}
+			get_task_struct(tsk);
+			rcu_read_unlock();
+			if (arg2 <= 0)
+				tsk->timer_slack_ns =
+					tsk->default_timer_slack_ns;
+			else
+				tsk->timer_slack_ns = arg2;
+			put_task_struct(tsk);
+			error = 0;
+			break;
 		default:
 			error = -EINVAL;
 			break;