linux-kernel - Re: [Patch] lkdtm: avoid calling lkdtm_do

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Message-Id: <20120130125429.56f6f7d0.akpm@linux-foundation.org>
Date:	Mon, 30 Jan 2012 12:54:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	linux-kernel@...r.kernel.org, Prarit Bhargava <prarit@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <greg@...ah.com>
Subject: Re: [Patch] lkdtm: avoid calling lkdtm_do_action() with spin lock
 held

On Sat, 28 Jan 2012 20:52:47 +0800
Cong Wang <xiyou.wangcong@...il.com> wrote:

> lkdtm_do_action() may call sleeping functions like kmalloc(),
> so do not call it with spin lock held.
> 
> Cc: Prarit Bhargava <prarit@...hat.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@...il.com>
> 
> ---
> diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
> index 150cd70..28adefe 100644
> --- a/drivers/misc/lkdtm.c
> +++ b/drivers/misc/lkdtm.c
> @@ -354,6 +354,7 @@ static void lkdtm_do_action(enum ctype which)
>  static void lkdtm_handler(void)
>  {
>  	unsigned long flags;
> +	bool do_it = false;
>  
>  	spin_lock_irqsave(&count_lock, flags);
>  	count--;
> @@ -361,10 +362,13 @@ static void lkdtm_handler(void)
>  			cp_name_to_str(cpoint), cp_type_to_str(cptype), count);
>  
>  	if (count == 0) {
> -		lkdtm_do_action(cptype);
> +		do_it = true;
>  		count = cpoint_count;
>  	}
>  	spin_unlock_irqrestore(&count_lock, flags);
> +
> +	if (do_it)
> +		lkdtm_do_action(cptype);
>  }
>  
>  static int lkdtm_register_cpoint(enum cname which)

lkdtm_handler() can be called from module IRQ handlers, so perhaps the
same problems can still happen.  The patch does improve things though ;)

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