linux-kernel - Re: [PATCH] Lockdep treats down_write_trylock like regular down

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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@...ux.intel.com>
To:	Pavel Emelianov <xemul@...ru>
CC:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Lockdep treats down_write_trylock like regular down_write

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...
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