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

From: Ingo Molnar <[email-masked]>
Date: Fri, 21 Nov 2008 17:37:17 +0100

* Joerg Roedel <[email-masked]> 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.

	Ingo