linux-kernel - Re: [PATCH 08/16] dma-debug: add core checking functions

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Message-ID: <20090110231127.GK17917@elte.hu>
Date:	Sun, 11 Jan 2009 00:11:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	dwmw2@...radead.org, fujita.tomonori@....ntt.co.jp,
	netdev@...r.kernel.org, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 08/16] dma-debug: add core checking functions


* Joerg Roedel <joerg.roedel@....com> wrote:

> +#define err_printk(dev, format, arg...) do {			\
> +		error_count += 1;				\
> +		if (show_all_errors || show_num_errors > 0) {	\
> +			WARN(1, "%s %s: " format,		\
> +			     dev_driver_string(dev),		\
> +			     dev_name(dev) , ## arg);		\
> +		}						\
> +		if (!show_all_errors && show_num_errors > 0)	\
> +			show_num_errors -= 1;			\

Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket 
so if two errors hit at once on two CPUs then the error tracking variables 
can be accessed at once.

I'd suggest a simple global lock for this error case (taken inside the 
hash bucket lock), to be on the safe side.

Also, please dont use a macro for this - printk details can be passed in 
to helper inlines/functions too.

	Ingo
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