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

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Message-ID: <20090114114829.GI8625@elte.hu>
Date:	Wed, 14 Jan 2009 12:48:29 +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:

> On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote:
> > 
> > * 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.
> 
> As I wrote in a previous email, a race here is no big deal. I add a 
> comment to document it. Or do we want another global lock here?

we commonly use global locks in debug exception cases - to serialize 
console output. But it's certainly no big deal.

	Ingo
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