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

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

[Gene Heskett]

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?

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
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by Gene Heskett are:
Copyright 2004 by Maurice Eugene Heskett, all rights reserved.

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

[Andrew Morton]

Gene Heskett <gene.heskett@verizon.net> 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.