lkml.org 
[lkml]   [2009]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 03/16] dma-debug: add hash functions for dma_debug_entries
From
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.


\
 
 \ /
  Last update: 2009-01-15 04:49    [W:0.143 / U:0.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site