[patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

[patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

[Thomas Gleixner]

[-- Attachment #1: oom-fix-missing-rcu-protection-of-__task_cred.patch --]
[-- Type: text/plain, Size: 1220 bytes --]

dump_tasks accesses __task_cred() without being in a RCU read side
critical section. tasklist_lock is not protecting that when
CONFIG_TREE_PREEMPT_RCU=y.

Add a rcu_read_lock/unlock() section around the code which accesses
__task_cred().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
---
 mm/oom_kill.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6-tip/mm/oom_kill.c
===================================================================
--- linux-2.6-tip.orig/mm/oom_kill.c
+++ linux-2.6-tip/mm/oom_kill.c
@@ -329,10 +329,13 @@ static void dump_tasks(const struct mem_
 			task_unlock(p);
 			continue;
 		}
+		/* Protect __task_cred() access */
+		rcu_read_lock();
 		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
 		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
 		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
 		       p->comm);
+		rcu_read_unlock();
 		task_unlock(p);
 	} while_each_thread(g, p);
 }


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

[KOSAKI Motohiro]

> dump_tasks accesses __task_cred() without being in a RCU read side
> critical section. tasklist_lock is not protecting that when
> CONFIG_TREE_PREEMPT_RCU=y.
> 
> Add a rcu_read_lock/unlock() section around the code which accesses
> __task_cred().
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-mm@kvack.org
> ---
>  mm/oom_kill.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6-tip/mm/oom_kill.c
> ===================================================================
> --- linux-2.6-tip.orig/mm/oom_kill.c
> +++ linux-2.6-tip/mm/oom_kill.c
> @@ -329,10 +329,13 @@ static void dump_tasks(const struct mem_
>  			task_unlock(p);
>  			continue;
>  		}
> +		/* Protect __task_cred() access */
> +		rcu_read_lock();
>  		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
>  		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
>  		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
>  		       p->comm);
> +		rcu_read_unlock();
>  		task_unlock(p);
>  	} while_each_thread(g, p);
>  }

Looks straight forward and correct to me.

	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

[David Howells]

Thomas Gleixner <tglx@linutronix.de> wrote:

> +		/* Protect __task_cred() access */
> +		rcu_read_lock();
>  		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
>  		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
>  		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
>  		       p->comm);
> +		rcu_read_unlock();

No.  If there's only one access to __task_cred() like this, use
task_cred_xxx() or one of its wrappers instead:

-		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
+		       p->pid, task_uid(p), p->tgid, mm->total_vm,

that limits the size of the critical section.

David

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [patch 4/9] oom: Add missing rcu protection of __task_cred() in dump_tasks

[Thomas Gleixner]

On Fri, 11 Dec 2009, David Howells wrote:

> Thomas Gleixner <tglx@linutronix.de> wrote:
> 
> > +		/* Protect __task_cred() access */
> > +		rcu_read_lock();
> >  		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
> >  		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
> >  		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
> >  		       p->comm);
> > +		rcu_read_unlock();
> 
> No.  If there's only one access to __task_cred() like this, use
> task_cred_xxx() or one of its wrappers instead:
> 
> -		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
> +		       p->pid, task_uid(p), p->tgid, mm->total_vm,
> 
> that limits the size of the critical section.

Fair enough.

     tglx

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>