From: Matt Helsley <matthltc@us.ibm.com>

Adapts delayacct to use Task Watchers.  Does not adapt taskstats to use Task
Watchers.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Chandra S. Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 include/linux/delayacct.h |    2 +-
 kernel/delayacct.c        |   23 +++++++++++++++++++++++
 kernel/exit.c             |    2 --
 kernel/fork.c             |    2 --
 4 files changed, 24 insertions(+), 5 deletions(-)

diff -puN include/linux/delayacct.h~task-watchers-register-per-task-delay-accounting include/linux/delayacct.h
--- a/include/linux/delayacct.h~task-watchers-register-per-task-delay-accounting
+++ a/include/linux/delayacct.h
@@ -61,7 +61,7 @@ static inline void delayacct_tsk_init(st
 
 static inline void delayacct_tsk_exit(struct task_struct *tsk)
 {
-	if (tsk->delays)
+	if (unlikely(tsk->delays))
 		__delayacct_tsk_exit(tsk);
 }
 
diff -puN kernel/delayacct.c~task-watchers-register-per-task-delay-accounting kernel/delayacct.c
--- a/kernel/delayacct.c~task-watchers-register-per-task-delay-accounting
+++ a/kernel/delayacct.c
@@ -18,6 +18,7 @@
 #include <linux/time.h>
 #include <linux/sysctl.h>
 #include <linux/delayacct.h>
+#include <linux/notifier.h>
 
 int delayacct_on __read_mostly;	/* Delay accounting turned on/off */
 kmem_cache_t *delayacct_cache;
@@ -29,6 +30,27 @@ static int __init delayacct_setup_enable
 }
 __setup("delayacct", delayacct_setup_enable);
 
+static int delayacct_watch_task(struct notifier_block *nb, unsigned long val,
+				void *t)
+{
+	struct task_struct *tsk = t;
+	switch(get_watch_event(val)) {
+	case WATCH_TASK_CLONE:
+		delayacct_tsk_init(tsk);
+		break;
+	case WATCH_TASK_FREE:
+		delayacct_tsk_exit(tsk);
+		break;
+	default:
+		return NOTIFY_DONE;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __read_mostly delayacct_nb = {
+	.notifier_call = delayacct_watch_task,
+};
+
 void delayacct_init(void)
 {
 	delayacct_cache = kmem_cache_create("delayacct_cache",
@@ -36,6 +58,7 @@ void delayacct_init(void)
 					0,
 					SLAB_PANIC,
 					NULL, NULL);
+	register_task_watcher(&delayacct_nb);
 	delayacct_tsk_init(&init_task);
 }
 
diff -puN kernel/exit.c~task-watchers-register-per-task-delay-accounting kernel/exit.c
--- a/kernel/exit.c~task-watchers-register-per-task-delay-accounting
+++ a/kernel/exit.c
@@ -28,7 +28,6 @@
 #include <linux/proc_fs.h>
 #include <linux/mempolicy.h>
 #include <linux/taskstats_kern.h>
-#include <linux/delayacct.h>
 #include <linux/cpuset.h>
 #include <linux/syscalls.h>
 #include <linux/signal.h>
@@ -910,7 +909,6 @@ fastcall NORET_TYPE void do_exit(long co
 	tsk->exit_code = code;
 	taskstats_exit_send(tsk, tidstats, group_dead);
 	taskstats_exit_free(tidstats);
-	delayacct_tsk_exit(tsk);
 	notify_result = notify_watchers(WATCH_TASK_FREE, tsk);
 	WARN_ON(notify_result & NOTIFY_STOP_MASK);
 
diff -puN kernel/fork.c~task-watchers-register-per-task-delay-accounting kernel/fork.c
--- a/kernel/fork.c~task-watchers-register-per-task-delay-accounting
+++ a/kernel/fork.c
@@ -44,7 +44,6 @@
 #include <linux/profile.h>
 #include <linux/rmap.h>
 #include <linux/acct.h>
-#include <linux/delayacct.h>
 #include <linux/taskstats_kern.h>
 
 #include <asm/pgtable.h>
@@ -1006,7 +1005,6 @@ static task_t *copy_process(unsigned lon
 		goto bad_fork_cleanup_put_domain;
 
 	p->did_exec = 0;
-	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
 	copy_flags(clone_flags, p);
 	p->pid = pid;
 	retval = -EFAULT;
_