linux-kernel - Re: suspicious rcu_dereference

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Date:	Tue, 9 Nov 2010 11:09:31 +0200
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, sergey.senozhatsky@...il.com
Subject: Re: suspicious rcu_dereference_check() usage splat

On (11/08/10 12:24), Paul E. McKenney wrote:
> Looking over the patch again, the scope of the RCU read-side critical
> section needs to expand to cover the use of the pointer as well as the
> call to find_task_by_vpid().  So, for example:
> 
> 		case IOPRIO_WHO_PROCESS:
> 			rcu_read_lock();
> 			if (!who)
> 				p = current;
> 			else
> 				p = find_task_by_vpid(who);
> 			if (p)
> 				ret = set_task_ioprio(p, ioprio);
> 			rcu_read_unlock();
> 			break;
> 		case IOPRIO_WHO_PGRP:
> 
> 
> Otherwise, the task could go away before the last use.
> 
> Sergey, could you please make this change and re-post your patch?
> 
> 							Thanx, Paul
> 

Hello,
Should we protect set_task_ioprio? Critical operations are protected
with rcu_read_lock/rcu_read_unlock in set_task_ioprio, the rest is protected
via task_lock(task)/task_unlock(task).

	Sergey

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