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Message-ID: <461A5733.3080303@linux.intel.com>
Date: Mon, 09 Apr 2007 08:09:39 -0700
From: Arjan van de Ven <arjan@linux.intel.com>
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To: Pavel Emelianov <xemul@sw.ru>
CC: Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Lockdep treats down_write_trylock like regular down_write
References: <461A0DDC.5060709@sw.ru>
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Pavel Emelianov wrote:
> This causes constructions like
> 
> down_write(&mm1->mmap_sem);
> if (down_write_trylock(&mm2->mmap_sem)) {
>        ...
>        up_write(&mm2->mmap_sem);
> }
> up_write(&mm1->mmap_sem);
> 
> generate a lockdep warning about circular locking dependence.

please show me why this is safe, especially if you intermix it with 
down_read()'s... like copy_to_user and co may do.

this feels like a very unsafe construct to me...