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Date: Wed, 4 Feb 2009 20:43:39 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Mandeep Singh Baines <msb@google.com>
Cc: =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
       Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
       rientjes@google.com, mbligh@google.com, thockin@google.com,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/2 v3] softlockup: check all tasks in hung_task
Message-ID: <20090204194339.GB22608@elte.hu>
References: <20090203122346.GE19979@elte.hu> <20090203205609.GA9581@google.com>
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* Mandeep Singh Baines <msb@google.com> wrote:

> +static void check_hung_rcu_refresh(struct task_struct *g, struct task_struct *t)

please rename this to rcu_lock_break().

>  	do_each_thread(g, t) {
> -		if (!--max_count)
> -			goto unlock;
> +		if (!--max_count) {
> +			max_count = sysctl_hung_task_check_count;
> +			check_hung_rcu_refresh(g, t);
> +			/* Exit if t or g was unhashed during refresh. */
> +			if (t->state == TASK_DEAD || g->state == TASK_DEAD)
> +				goto unlock;

Thinking about it some more, i think a slightly different approach (that has 
the same end effect):

 - Add a "static const int check_count_batching = 1024;" variable that adds 
   some natural batching - and initialize max_count to that value. There's 
   little point to make that batching configurable.

 - Leave sysctl_hung_task_check_count present but change its default to 
   something really large like MAX_PID.

Thanks,

	Ingo