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

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Date:	Fri, 13 Oct 2006 14:10:34 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Helge Hafting <helge.hafting@...el.hist.no>,
	Andrew Morton <akpm@...l.org>
cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] 2.6.19-rc1-mm1 - locks when using "dd bs=1M"
 from card reader

On Fri, 13 Oct 2006, Andrew Morton wrote:

> 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?

Verbose usb-storage debugging messages would help more 
(CONFIG_USB_STORAGE_DEBUG and CONFIG_USB_DEBUG).  If the kernel hangs very 
badly you might need to use a serial console to capture all the logging 
information.

Alan Stern

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