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SubjectRe: [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@aitel.hist.no> wrote:
>
> > Andrew Morton wrote:
> > > On Thu, 12 Oct 2006 14:18:04 +0200
> > > Helge Hafting <helge.hafting@aitel.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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