linux-kernel - Re: [PATCH] ioprio: rcu_read_lock/unlock protect find_task_by

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Date:	Tue, 9 Nov 2010 21:20:50 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
CC:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH] ioprio: rcu_read_lock/unlock protect find_task_by_vpid
  call (V2)

On 2010-11-09 21:15, Paul E. McKenney wrote:
> On Tue, Nov 09, 2010 at 12:21:24PM +0200, Sergey Senozhatsky wrote:
>> Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for
>> find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns..
>> Assertion failed in sys_ioprio_get. The patch is fixing assertion
>> failure in ioprio_set as well.
>>
>>  kernel/pid.c:419 invoked rcu_dereference_check() without protection!
>>
>>  stack backtrace:
>>  Pid: 4254, comm: iotop Not tainted
>>  Call Trace:
>>  [<ffffffff810656f2>] lockdep_rcu_dereference+0xaa/0xb2
>>  [<ffffffff81053c67>] find_task_by_pid_ns+0x4f/0x68
>>  [<ffffffff81053c9d>] find_task_by_vpid+0x1d/0x1f
>>  [<ffffffff811104e2>] sys_ioprio_get+0x50/0x2da
>>  [<ffffffff81002182>] system_call_fastpath+0x16/0x1b
>>                      
>> V2: rcu critical section expanded according to comment by Paul E. McKenne:
>> | 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().
> 
> Thank you, Sergey!
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Jens, are you willing to take this one?

Certainly, thanks guys!

-- 
Jens Axboe

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