[Devel] [PATCH, v6 2/3] Implement timer slack notifier chain

[Kirill A. Shutsemov]

From: Kirill A. Shutemov <kirill at shutemov.name>

Process can change its timer slack using prctl(). Timer slack notifier
call chain allows to react on such change or forbid it.

Signed-off-by: Kirill A. Shutemov <kirill at shutemov.name>
---
 include/linux/sched.h |    5 ++++
 kernel/Makefile       |    2 +-
 kernel/sys.c          |    9 +------
 kernel/timer_slack.c  |   57 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 65 insertions(+), 8 deletions(-)
 create mode 100644 kernel/timer_slack.c

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d747f94..f1a4ec2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2620,6 +2620,11 @@ static inline unsigned long rlimit_max(unsigned int limit)
 	return task_rlimit_max(current, limit);
 }
 
+extern int register_timer_slack_notifier(struct notifier_block *nb);
+extern void unregister_timer_slack_notifier(struct notifier_block *nb);
+long prctl_get_timer_slack(void);
+extern long prctl_set_timer_slack(long timer_slack_ns);
+
 #endif /* __KERNEL__ */
 
 #endif
diff --git a/kernel/Makefile b/kernel/Makefile
index 353d3fe..aa43e63 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -10,7 +10,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o \
 	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
 	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
 	    notifier.o ksysfs.o pm_qos_params.o sched_clock.o cred.o \
-	    async.o range.o jump_label.o
+	    async.o range.o jump_label.o timer_slack.o
 obj-y += groups.o
 
 ifdef CONFIG_FUNCTION_TRACER
diff --git a/kernel/sys.c b/kernel/sys.c
index 18da702..a33e4b8 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1691,15 +1691,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			error = perf_event_task_enable();
 			break;
 		case PR_GET_TIMERSLACK:
-			error = current->timer_slack_ns;
+			error = prctl_get_timer_slack();
 			break;
 		case PR_SET_TIMERSLACK:
-			if (arg2 <= 0)
-				current->timer_slack_ns =
-					current->default_timer_slack_ns;
-			else
-				current->timer_slack_ns = arg2;
-			error = 0;
+			error = prctl_set_timer_slack(arg2);
 			break;
 		case PR_MCE_KILL:
 			if (arg4 | arg5)
diff --git a/kernel/timer_slack.c b/kernel/timer_slack.c
new file mode 100644
index 0000000..546ed78
--- /dev/null
+++ b/kernel/timer_slack.c
@@ -0,0 +1,57 @@
+/*
+ * kernel/timer_slack.c
+ *
+ * Copyright Nokia Corparation, 2011
+ * Author: Kirill A. Shutemov
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/notifier.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+
+static BLOCKING_NOTIFIER_HEAD(timer_slack_notify_list);
+
+int register_timer_slack_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&timer_slack_notify_list, nb);
+}
+EXPORT_SYMBOL_GPL(register_timer_slack_notifier);
+
+void unregister_timer_slack_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&timer_slack_notify_list, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_timer_slack_notifier);
+
+long prctl_get_timer_slack(void)
+{
+	return current->timer_slack_ns;
+}
+
+long prctl_set_timer_slack(long timer_slack_ns)
+{
+	int err;
+
+	/* Reset timer slack to default value */
+	if (timer_slack_ns <= 0) {
+		current->timer_slack_ns = current->default_timer_slack_ns;
+		return 0;
+	}
+
+	err = blocking_notifier_call_chain(&timer_slack_notify_list,
+			timer_slack_ns, NULL);
+	if (err == NOTIFY_DONE)
+		current->timer_slack_ns = timer_slack_ns;
+
+	return notifier_to_errno(err);
+}
-- 
1.7.4

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