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

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Date:	Thu, 8 Apr 2010 16:20:00 +0800
From:	Liang Li <liang.li@...driver.com>
To:	Yong Zhang <yong.zhang@...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 03:50:03PM +0800, Yong Zhang wrote:
> 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));
> >  }

Seems what I saw was different from this bug. So it is clear
that this one line change does not relate to this bug. Sorry
for confusion.

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

Thanks,
		-Liang Li
> 
> 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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