linux-kernel - Re: [PATCH] lockdep: Avoid /proc/lockdep & lock

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Date:	Tue, 9 Oct 2007 02:30:11 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lockdep: Avoid /proc/lockdep & lock_stat infinite output

On Mon, Oct 08, 2007 at 06:15:51PM -0700, Tim Pepper wrote:
> 
> When a read() requests an amount of data smaller than the amount of data
> that the seq_file's foo_show() outputs, the output starts looping and
> outputs the "stuck" element's data infinitely.  There may be multiple
> sequential calls to foo_start(), foo_next()/foo_show(), and foo_stop()
> for a single open with sequential read of the file.  The _start() does not
> have to start with the 0th element and _show() might be called multiple
> times in a row for the same element for a given open/read of the seq_file.
>  
>  static void *l_start(struct seq_file *m, loff_t *pos)
>  {
> -	struct lock_class *class = m->private;
> +	struct lock_class *class;
> +	loff_t i = 0;
>  
> -	if (&class->lock_entry == all_lock_classes.next)
> +	if (*pos == 0)
>  		seq_printf(m, "all lock classes:\n");

Do not generate output outside of ->show() and you won't have these
problems.  That's where your infinite output crap comes from.

IOW, NAK - fix the underlying problem.
-
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