linux-kernel - Re: [Bug #15615] NULL pointer deref in task_is

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Date:	Thu, 8 Apr 2010 15:50:03 +0800
From:	Yong Zhang <yong.zhang@...driver.com>
To:	Liang Li <liang.li@...driver.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Amit Shah <shahamit@...il.com>
Subject: Re: [Bug #15615] NULL pointer deref in task_is_waking

On Thu, Apr 08, 2010 at 03:16:17PM +0800, Liang Li wrote:
> On Wed, Apr 07, 2010 at 11:13:48PM +0200, Rafael J. Wysocki wrote:
> > This message has been generated automatically as a part of a summary report
> > of recent regressions.
> > 
> > The following bug entry is on the current list of known regressions
> > from 2.6.33.  Please verify if it still should be listed and let the tracking team
> > know (either way).
> 
> The bug still there. I just met it. And seems its quite simple to get it
> fixed.
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index a3dff1f..2df1a76 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -913,7 +913,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
>   */
>  static inline int task_is_waking(struct task_struct *p)
>  {
> -	return unlikely((p->state == TASK_WAKING) && !(p->flags & PF_STARTING));
> +	return unlikely(p && (p->state == TASK_WAKING) && !(p->flags & PF_STARTING));
>  }

Oh, NO. This is wrong. It will introduce other bugs.
The right direction is showed in the bug entry.

Thanks,
Yong

>  
>  /*
> 
> But seems commitid 0017d735092844118bef006696a750a0e4ef6ebd in tip tree
> also touched task_is_waking. So the patch for tip tree should be:
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 3acf694..d259641 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -920,7 +920,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
>   */
>  static inline int task_is_waking(struct task_struct *p)
>  {
> -	return unlikely(p->state == TASK_WAKING);
> +	return unlikely(p && p->state == TASK_WAKING);
>  }
>  
>  /*
> 
> Regards,
> 	-Liang Li
> 
> > 
> > 
> > Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=15615
> > Subject		: NULL pointer deref in task_is_waking
> > Submitter	: Amit Shah <shahamit@...il.com>
> > Date		: 2010-03-23 04:04 (16 days old)
> > 
> > 
> > --
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