From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
To: mingo@elte.hu
Cc: akpm@linux-foundation.org, joerg.roedel@amd.com,
linux-kernel@vger.kernel.org, mingo@redhat.com,
dwmw2@infradead.org, fujita.tomonori@lab.ntt.co.jp,
netdev@vger.kernel.org, iommu@lists.linux-foundation.org
Subject: Re: [PATCH 03/16] dma-debug: add hash functions for dma_debug_entries
Date: Thu, 15 Jan 2009 12:44:35 +0900 [thread overview]
Message-ID: <20090115124441V.fujita.tomonori@lab.ntt.co.jp> (raw)
In-Reply-To: <20090114174804.GB31983@elte.hu>
On Wed, 14 Jan 2009 18:48:04 +0100
Ingo Molnar <mingo@elte.hu> wrote:
>
> * 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.
We have had ugly DMA bugs in scsi drivers but I think that this new
feature can find very few of them. I can't think of any SCSI driver
bugs that this could find. This feature can't find any popular DMA
bugs in scsi drivers, such as messing up driver's dma descriptor from
a scatter gather list.
But this can find some kinds of DMA bugs and it's is just about 1,000
lines. I don't see any problem about merging this. 1,000 lines it too
large? Maybe cutting just 1,000 lines up into too many pieces is
deceptive.
next prev parent reply other threads:[~2009-01-15 3:45 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-09 16:19 [PATCH 0/16] DMA-API debugging facility v2 Joerg Roedel
2009-01-09 16:19 ` [PATCH 01/16] dma-debug: add Kconfig entry Joerg Roedel
2009-01-09 20:12 ` Randy Dunlap
2009-01-09 16:19 ` [PATCH 02/16] dma-debug: add header file and core data structures Joerg Roedel
2009-01-11 6:25 ` FUJITA Tomonori
2009-01-09 16:19 ` [PATCH 03/16] dma-debug: add hash functions for dma_debug_entries Joerg Roedel
2009-01-09 17:55 ` Evgeniy Polyakov
2009-01-09 18:14 ` Joerg Roedel
2009-01-09 18:23 ` Evgeniy Polyakov
2009-01-09 18:40 ` Joerg Roedel
2009-01-13 8:51 ` Andrew Morton
2009-01-13 8:59 ` David Woodhouse
2009-01-14 11:43 ` Ingo Molnar
2009-01-14 17:39 ` Andrew Morton
2009-01-14 17:43 ` Ingo Molnar
2009-01-14 17:48 ` Ingo Molnar
2009-01-15 3:44 ` FUJITA Tomonori [this message]
2009-01-14 17:48 ` David Woodhouse
2009-01-14 17:51 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 04/16] dma-debug: add allocator code Joerg Roedel
2009-01-10 23:43 ` Ingo Molnar
2009-01-09 16:19 ` [PATCH 05/16] dma-debug: add initialization code Joerg Roedel
2009-01-09 17:58 ` Evgeniy Polyakov
2009-01-09 18:17 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 06/16] dma-debug: add kernel command line parameters Joerg Roedel
2009-01-09 16:19 ` [PATCH 07/16] dma-debug: add debugfs interface Joerg Roedel
2009-01-10 23:08 ` Ingo Molnar
2009-01-11 7:52 ` Joerg Roedel
2009-01-14 15:22 ` Joerg Roedel
2009-01-10 23:15 ` Ingo Molnar
2009-01-09 16:19 ` [PATCH 08/16] dma-debug: add core checking functions Joerg Roedel
2009-01-10 23:11 ` Ingo Molnar
2009-01-11 7:57 ` Joerg Roedel
2009-01-11 8:34 ` Joerg Roedel
2009-01-14 11:44 ` Joerg Roedel
2009-01-14 11:48 ` Ingo Molnar
2009-01-10 23:12 ` Ingo Molnar
2009-01-11 7:54 ` Joerg Roedel
2009-01-10 23:13 ` Ingo Molnar
2009-01-09 16:19 ` [PATCH 09/16] dma-debug: add checking for map/unmap_single Joerg Roedel
2009-01-09 16:19 ` [PATCH 10/16] dma-debug: add add checking for map/unmap_sg Joerg Roedel
2009-01-09 18:08 ` Evgeniy Polyakov
2009-01-09 18:11 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 11/16] dma-debug: add checking for [alloc|free]_coherent Joerg Roedel
2009-01-11 6:25 ` FUJITA Tomonori
2009-01-11 6:30 ` FUJITA Tomonori
2009-01-11 7:59 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 12/16] dma-debug: add checks for sync_single_* Joerg Roedel
2009-01-09 16:19 ` [PATCH 13/16] dma-debug: add checks for sync_single_range_* Joerg Roedel
2009-01-09 16:19 ` [PATCH 14/16] dma-debug: add checks for sync_single_sg_* Joerg Roedel
2009-01-10 23:46 ` Ingo Molnar
2009-01-11 8:00 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 15/16] dma-debug: x86 architecture bindings Joerg Roedel
2009-01-10 23:04 ` Ingo Molnar
2009-01-10 23:48 ` Ingo Molnar
2009-01-11 6:25 ` FUJITA Tomonori
2009-01-11 8:08 ` Joerg Roedel
2009-01-09 16:19 ` [PATCH 16/16] dma-debug: Documentation update Joerg Roedel
2009-01-09 21:24 ` [PATCH 0/16] DMA-API debugging facility v2 Michael Chan
2009-01-09 22:33 ` Joerg Roedel
2009-01-09 22:37 ` Joerg Roedel
2009-01-11 6:25 ` FUJITA Tomonori
2009-01-10 23:54 ` Ingo Molnar
2009-01-11 8:11 ` Joerg Roedel
2009-02-05 22:52 ` David Woodhouse
2009-02-06 2:05 ` Chris Wright
2009-02-06 7:56 ` David Woodhouse
2009-02-06 16:08 ` Chris Wright
2009-02-06 18:20 ` Chris Wright
2009-02-12 14:48 ` Joerg Roedel
2009-02-06 2:27 ` Chris Wright
2009-02-12 15:20 ` Joerg Roedel
2009-01-19 14:46 [PATCH 0/16] DMA-API debugging facility v3 Joerg Roedel
2009-01-19 14:46 ` [PATCH 03/16] dma-debug: add hash functions for dma_debug_entries Joerg Roedel
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