linux-kernel - Re: [PATCH] "volatile considered harmful", take 2

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Date:	Fri, 11 May 2007 09:41:26 +0200
From:	Philipp Matthias Hahn <pmhahn@...an.lahn.de>
To:	Jonathan Corbet <corbet@....net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] "volatile considered harmful", take 2

Hello!

On Thu, May 10, 2007 at 02:20:19PM -0600, Jonathan Corbet wrote:
...
> +++ b/Documentation/volatile-considered-harmful.txt
...
> +Consider a typical block of kernel code:
> +
> +    spin_lock(&the_lock);
> +    do_something_on(&shared_data);
                        ^^^^^^^^^^^
> +    do_something_else_with(&shared_data);
                               ^^^^^^^^^^^
> +    spin_unlock(&the_lock);
> +
> +If all the code follows the locking rules, the value of shared_data cannot
> +change unexpectedly while the_lock is held.  Any other code which might
> +want to play with that data will be waiting on the lock.  The spinlock
> +primitives act as memory barriers - they are explicitly written to do so -
> +meaning that data accesses will not be optimized across them.  So the
> +compiler might think it knows what will be in some_data, but the
s/some_data/shared_data/ ?                       ^^^^^^^^^

BYtE
Philipp
-- 
  / /  (_)__  __ ____  __ Philipp Hahn
 / /__/ / _ \/ // /\ \/ /
/____/_/_//_/\_,_/ /_/\_\ pmhahn@...an.lahn.de
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