linux-kernel - Re: Lockdep warning for sys

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Message-Id: <E1MTDyo-0002rz-FR@pomaz-ex.szeredi.hu>
Date:	Tue, 21 Jul 2009 13:57:58 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	peterz@...radead.org
CC:	eric.sesterhenn@...xperts.de, linux-kernel@...r.kernel.org,
	mingo@...hat.com, miklos@...redi.hu
Subject: Re: Lockdep warning for sys_tee system call

On Tue, 21 Jul 2009, Peter Zijlstra wrote:
> void pipe_double_lock(struct pipe_inode_info *pipe1,
> 		      struct pipe_inode_info *pipe2)
> {
> 	BUG_ON(pipe1 == pipe2);
> 
> 	if (pipe1 < pipe2) {
> 		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
> 		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
> 	} else {
> 		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
> 		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
> 	}
> }
> 
> That's an obvious FAIL right there.
> 
> Miklos?

Right, copy-paste bug.  At least I got the locking right ;)

Acked-by: Miklos Szeredi <mszeredi@...e.cz>

Thanks,
Miklos

> 
> ---
> Subject: fs/pipe: rectify a lockdep annotation
> 
> The presumed use of the pipe_double_lock() routine is to lock 2 locks in
> a deadlock free way by ordering the locks by their address. However it
> fails to keep the specified lock classes in order and explicitly
> annotates a deadlock.
> 
> Rectify this.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  fs/pipe.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/pipe.c b/fs/pipe.c
> index f7dd21a..52c4151 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -68,8 +68,8 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
>  		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
>  		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
>  	} else {
> -		pipe_lock_nested(pipe2, I_MUTEX_CHILD);
> -		pipe_lock_nested(pipe1, I_MUTEX_PARENT);
> +		pipe_lock_nested(pipe2, I_MUTEX_PARENT);
> +		pipe_lock_nested(pipe1, I_MUTEX_CHILD);
>  	}
>  }
>  
> 
> 
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