Messages in this thread | | | Date | Wed, 14 Jan 2009 18:48:04 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 03/16] dma-debug: add hash functions for dma_debug_entries |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 14 Jan 2009 12:43:47 +0100 Ingo Molnar <mingo@elte.hu> wrote: > > > > > * Andrew Morton <akpm@linux-foundation.org> wrote: > > > > > On Fri, 9 Jan 2009 17:19:17 +0100 Joerg Roedel <joerg.roedel@amd.com> wrote: > > > > > > > +struct hash_bucket { > > > > + struct list_head list; > > > > + spinlock_t lock; > > > > +} ____cacheline_aligned; > > > > > > __cacheline_aligned_in_smp. > > > > > > This all looks like an exotically large amount of code for a debug > > > thingy? > > > > this code checks the DMA usage of ~1 million lines of kernel code - all > > the DMA using drivers. I think Joerg's feature is hugely relevant as DMA > > scribbles are one of the hardest to debug kernel bugs: they can end up in > > permanent data corruption or other hard to find bugs. In fact i think his > > patchset is rather simple and even having 10 times as much debug code > > would pay for its existence in the long run. > > > > Have we previously found bugs by other means which this facility would > have detected? I don't recall any...
btw., during the past decade we have had countless very ugly driver DMA bugs in the past that took vendors months and specialized equipment to track down.
I cannot give you a number breakdown, only an impression: storage drivers tended to be the hardest hit (due to the severity of the bugs and due to their inherent complexity) - but DMA bugs in networking drivers can be hard to track down too.
Plus there's another benefit: if a driver passes this checking and there's still DMA related corruption observed, then the hardware / firmware becomes a stronger suspect. This helps debugging too.
Ingo
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