[PATCH -mm 4/4] oom: oom_forkbomb_penalty: movethread_group_cputime() out of task_lock()

[Oleg Nesterov]

It doesn't make sense to call thread_group_cputime() under task_lock(),
we can drop this lock right after we read get_mm_rss() and save the
value in the local variable.

Note: probably it makes more sense to use sum_exec_runtime instead
of utime + stime, it is much more precise. A task can eat a lot of
CPU time, but its Xtime can be zero.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---

 mm/oom_kill.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- MM/mm/oom_kill.c~4_FORKBOMB_DROP_TASK_LOCK_EARLIER	2010-04-02 19:55:46.000000000 +0200
+++ MM/mm/oom_kill.c	2010-04-02 20:16:13.000000000 +0200
@@ -110,13 +110,16 @@ static unsigned long oom_forkbomb_penalt
 		return 0;
 	list_for_each_entry(child, &tsk->children, sibling) {
 		struct task_cputime task_time;
-		unsigned long runtime;
+		unsigned long runtime, rss;
 
 		task_lock(child);
 		if (!child->mm || child->mm == tsk->mm) {
 			task_unlock(child);
 			continue;
 		}
+		rss = get_mm_rss(child->mm);
+		task_unlock(child);
+
 		thread_group_cputime(child, &task_time);
 		runtime = cputime_to_jiffies(task_time.utime) +
 			  cputime_to_jiffies(task_time.stime);
@@ -126,10 +129,9 @@ static unsigned long oom_forkbomb_penalt
 		 * get to execute at all in such cases anyway.
 		 */
 		if (runtime < HZ) {
-			child_rss += get_mm_rss(child->mm);
+			child_rss += rss;
 			forkcount++;
 		}
-		task_unlock(child);
 	}
 
 	/*

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