linux-kernel - Re: [PATCH v3] softlockup: remove hung_task_check

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Message-ID: <20090124025618.GB31189@google.com>
Date:	Fri, 23 Jan 2009 18:56:18 -0800
From:	Mandeep Singh Baines <msb@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	fweisbec@...il.com, linux-kernel@...r.kernel.org,
	rientjes@...gle.com, mbligh@...gle.com, thockin@...gle.com
Subject: Re: [PATCH v3] softlockup: remove hung_task_check_count

Ingo Molnar (mingo@...e.hu) wrote:
> 
> not sure i like the whole idea of removing the max iterations check. In 
> theory if there's a _ton_ of tasks, we could spend a lot of time looping 
> there. So it always looked prudent to limit it somewhat.
> 

We could go back to exporting max iterations to proc, and set the nice
value higher.

Or:

Instead of searching the tasklist from the beginning every time, continue
where you left off. On loaded systems, will take a while to search the
entire list but at least all tasks will be checked.

Something like this:

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index ba8ccd4..d220796 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -109,6 +109,15 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
 		panic("hung_task: blocked tasks");
 }
 
+static void wait_till_next_iteration(struct task_struct *t)
+{
+	get_task_state(t);
+	read_unlock(&tasklist_lock);
+	schedule_timeout_interruptible(hung_task_poll_jiffies);
+	read_lock(&tasklist_lock);
+	put_task_state(t);
+}
+
 /*
  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
  * a really long time (120 seconds). If that happens, print out
@@ -129,8 +138,14 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 
 	read_lock(&tasklist_lock);
 	do_each_thread(g, t) {
-		if (!--max_count)
-			goto unlock;
+		if (!--max_count) {
+			max_count = HUNG_TASK_CHECK_COUNT;
+			wait_till_next_iteration(t);
+			timeout = sysctl_hung_task_timeout_secs;
+			/* Exit loop if t was unlinked or timeout set to 0. */
+			if (!timeout || t->state == TASK_DEAD)
+				goto unlock;
+		}
 		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 		if (t->state == TASK_UNINTERRUPTIBLE)
 			check_hung_task(t, now, timeout);
--
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