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From: Andrew Morton <akpm@osdl.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Ingo Molnar <mingo@redhat.com>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org, ltt-dev@shafik.org,
	"Martin J. Bligh" <mbligh@mbligh.org>,
	Douglas Niehaus <niehaus@eecs.ku.edu>,
	systemtap@sources.redhat.com,
	Thomas Gleixner <tglx@linutronix.de>,
	Richard J Moore <richardj_moore@uk.ibm.com>
Subject: Re: [PATCH 1/2] lockdep missing barrier()
Date: Tue, 23 Jan 2007 20:26:37 -0800	[thread overview]
Message-ID: <20070123202637.970e467b.akpm@osdl.org> (raw)
In-Reply-To: <20070116175624.GA16022@Krystal>

On Tue, 16 Jan 2007 12:56:24 -0500
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

> This patch adds a barrier() to lockdep.c lockdep_recursion updates. This
> variable behaves like the preemption count and should therefore use similar
> memory barriers.
> 
> This patch applies on 2.6.20-rc4-git3.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> 
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -166,12 +166,14 @@ static struct list_head chainhash_table[CHAINHASH_SIZE];
>  void lockdep_off(void)
>  {
>  	current->lockdep_recursion++;
> +	barrier();
>  }
>  
>  EXPORT_SYMBOL(lockdep_off);
>  
>  void lockdep_on(void)
>  {
> +	barrier();
>  	current->lockdep_recursion--;
>  }

I am allergic to undocumented barriers.  It is often unobvious what the
barrier is supposed to protect against, yielding mystifying code.  This is
one such case.

Please add code comments.

  reply	other threads:[~2007-01-24  4:28 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-12-20 23:52 [PATCH 0/4] Linux Kernel Markers Mathieu Desnoyers
2006-12-20 23:57 ` [PATCH 1/4] Linux Kernel Markers : Architecture agnostic code Mathieu Desnoyers
2006-12-20 23:59 ` [PATCH 2/4] Linux Kernel Markers : kconfig menus Mathieu Desnoyers
2006-12-21  0:00 ` [PATCH 3/4] Linux Kernel Markers : i386 optimisation Mathieu Desnoyers
2006-12-21  0:01 ` [PATCH 4/4] Linux Kernel Markers : powerpc optimisation Mathieu Desnoyers
2007-01-13  1:33 ` [PATCH 0/4] Linux Kernel Markers Richard J Moore
2007-01-13  5:45   ` Mathieu Desnoyers
2007-01-16 17:41     ` [PATCH 0/4 update] Linux Kernel Markers - i386 : pIII erratum 49 : XMC Mathieu Desnoyers
2007-01-16 18:35       ` Frank Ch. Eigler
2007-01-16 21:27       ` [PATCH 0/4 update] kprobes and traps Mathieu Desnoyers
2007-01-17 12:25         ` S. P. Prasanna
2007-01-16 17:56   ` [PATCH 1/2] lockdep missing barrier() Mathieu Desnoyers
2007-01-24  4:26     ` Andrew Morton [this message]
2007-01-24 16:51       ` Mathieu Desnoyers
2007-01-24 17:24         ` [PATCH] order of lockdep off/on in vprintk() should be changed Mathieu Desnoyers
2007-01-24 17:55           ` [PATCH] minimize lockdep_on/off side-effect Mathieu Desnoyers
2007-01-16 17:56   ` [PATCH 2/2] lockdep reentrancy Mathieu Desnoyers
2007-01-24  4:29     ` Andrew Morton
2007-01-24 16:55       ` Mathieu Desnoyers

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