linux-kernel - Re: [PATCH] hung_task: Allow hung_task_panic when hung_task

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Date:   Sat, 10 Sep 2016 09:18:08 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     akpm@...ux-foundation.org, jsiddle@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hung_task: Allow hung_task_panic when hung_task_warnings is 0.

Andrew Morton wrote:
> This introduces an off-by-one error.  In the old code, if
> sysctl_hung_task_warnings==1 on entry, we warn.  With the new code, we
> no longer warn.

Since sysctl_hung_task_warnings == -1 is allowed, we should not
sysctl_hung_task_warnings-- unless sysctl_hung_task_warnings > 0.

> 
> This?
> 
> --- a/kernel/hung_task.c~hung_task-allow-hung_task_panic-when-hung_task_warnings-is-0-fix
> +++ a/kernel/hung_task.c
> @@ -101,14 +101,12 @@ static void check_hung_task(struct task_
>  	if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
>  		return;
>  
> -	if (sysctl_hung_task_warnings > 0)
> -		sysctl_hung_task_warnings--;
> -
>  	/*
>  	 * Ok, the task did not get scheduled for more than 2 minutes,
>  	 * complain:
>  	 */
>  	if (sysctl_hung_task_warnings) {

+		if (sysctl_hung_task_warnings > 0)

> +		sysctl_hung_task_warnings--;
>  		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
>  			t->comm, t->pid, timeout);
>  		pr_err("      %s %s %.*s\n",