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Subject: Re: [PATCH] tty: tty_mutex: fix lockdep warning in
 tty_lock_pair(v3)
From: Peter Zijlstra <peterz@infradead.org>
To: Ming Lei <ming.lei@canonical.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, Alan Cox <alan@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>
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Date: Sat, 26 May 2012 18:39:45 +0200
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On Sat, 2012-05-26 at 17:23 +0800, Ming Lei wrote:
> 
> You mean that the below is good usage of lock?
> 
>         LOCK A
>         LOCK B
> 
>         UNLOCK A
>         UNLOCK B 

Yep, nothing wrong with that. Its lock order that matters, unlock very
much not so.