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

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Date:	Thu, 8 Apr 2010 15:16:17 +0800
From:	Liang Li <liang.li@...driver.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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 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));
 }
 
 /*

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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