linux-kernel - Re: 2.6.19-rc1-mm1 - locks when using "dd bs=1M" from card reader

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Date:	Fri, 13 Oct 2006 09:29:41 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Helge Hafting <helge.hafting@...el.hist.no>
Cc:	linux-kernel@...r.kernel.org, linux-usb-devel@...ts.sourceforge.net
Subject: Re: 2.6.19-rc1-mm1 - locks when using "dd bs=1M" from card reader

On Fri, 13 Oct 2006 15:11:11 +0200
Helge Hafting <helge.hafting@...el.hist.no> wrote:

> Andrew Morton wrote:
> > On Thu, 12 Oct 2006 14:18:04 +0200
> > Helge Hafting <helge.hafting@...el.hist.no> wrote:
> >
> >   
> >> I found an easy way to hang the kernel when copying a SD-card:
> >>
> >> dd if=/dev/sdc of=file bs=1048576
> >>
> >> I.e. copy the entire 256MB card in 1MB chunks.  I got about
> >> 160MB before the kernel hung.  Not even sysrq+B worked, I needed
> >> the reset button.  The pc has a total of 512MB memory if that matters.
> >>
> >> Using bs=4096 instead let me copy the entire card with no problems,
> >> but that seems to progress slower.
> >>
> >> The above 'dd' command hangs my office pc every time. So I can repeat
> >> it for debugging purposes. 
> >>
> >>     
> >
> > What device driver is providing /dev/sdc?
> >   
> It is an usb card reader, so it is "usb mass storage"
> and "scsi disk".
> > Did any previous kernels work correctly?  If so, which?
> >   
> 
> I just got that card reader, so I haven't tested any earlier kernels.
> I have another machine with a card reader, which I have used for
> a long time. But I only ever copy files with "cp" on that one.
> 
> This time I used "dd" to get an image of the entire card, and got trouble
> when using 1M chunks. 
> 
> I can try with verbose scsi debug messages if that might help?
> 

Maybe.  The first step is to tell the developers. (adds cc).

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