Re: odd problem with dd, kernels 2.6.5-mm6, 2.6.6 maybe others

From: Andrew Morton
Date: Thu May 13 2004 - 00:21:02 EST

Gene Heskett <gene.heskett@xxxxxxxxxxx> wrote:
> Greetings;
> I'm apparently having tape problems, and dd is one of the tools I use
> to fix things. Unforch, when /dev/nst0 has reported an error during
> the amcheck cycle, on 2 of the 4 tapes that it read just fine
> yesterday, and then I do a rewind on one of them, and issue a 'dd
> if=/dev/nst0 count=1' which *should* spit out the tape header
> onscreen, what I'm actually getting is that nothing touches the drive
> as far as moving the tape or changing the "Ready 1" display on the
> face of the changer, but I do have a hung dd that can only be gotten
> rid of by a reboot.
> It cannot be killed, not even with a -9. I do not know if this is a
> new development in kernel history or not, but it sure is a PITA.
> Its been hung for about 20 minutes now.
> Is there anything that I as a big dummy can do to remedy this?

Please ensure that the kernel was built with CONFIG_KALLSYMS, wait for the
hang, do:

echo 1 > /proc/sys/kernel/sysrq
dmesg -c > /dev/null
echo t > /proc/sysrq-trigger
dmesg -s 1000000 > foo

and send foo.
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