linux-kernel - Re: [PATCH 0/10] DMA-API debugging facility

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Date:	Fri, 21 Nov 2008 17:40:41 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 0/10] DMA-API debugging facility

On Fri, Nov 21, 2008 at 05:37:17PM +0100, Ingo Molnar wrote:
> 
> * Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > Hi,
> > 
> > this patchset introduces code to debug drivers usage of the DMA-API. 
> > Tests with hardware IOMMUs have shown several bugs in drivers 
> > regarding the usage of that API. Problems were found especially in 
> > network card drivers.
> > 
> > These bugs often don't show up or have any negative impact if there 
> > is no hardware IOMMU in use in the system. But with an hardware 
> > IOMMU these bugs turn the hardware unusable or, in the worst case, 
> > cause data corruption on devices which are managed by other (good) 
> > drivers.
> > 
> > With the code these patches introduce driver developers can find 
> > several bugs of misusing the DMA-API in their drivers. But be aware, 
> > it can not find all possible bugs. If it finds a problem it prints 
> > out messages like
> > 
> > tg3 0000:08:04.0: PCI-DMA: device driver tries to free DMA memory it 
> > has not allocated [device address=0x000000042f0f3ae7] [size=48 
> > bytes]
> >
> > Pid: 6285, comm: bash Not tainted 2.6.28-rc5-00176-g6ae6379-dirty #6
> > Call Trace:
> >  <IRQ>  [<ffffffff80221276>] check_unmap+0x52/0x1ce
> >  [<ffffffff80221af0>] debug_unmap_single+0x61/0xa4
> >  [<ffffffff8053d396>] skb_dma_unmap+0xf2/0x10c
> >  [<ffffffff8040a986>] tg3_poll+0xe8/0x822
> >  [<ffffffff803abe2f>] mix_pool_bytes_extract+0x5c/0x155
> >  [<ffffffff80540e42>] net_rx_action+0x9d/0x170
> 
> very nice! I like this approach - and have a few comments on some 
> details - will post them as a reply to the patchs.

Cool. Thank you.

Joerg

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