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Re: Fwd: Hurd shutdown problems

From: Justus Winter
Subject: Re: Fwd: Hurd shutdown problems
Date: Tue, 09 Aug 2016 09:32:56 +0200
User-agent: Notmuch/0.22+51~gcc1a6d2 (https://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu)


"Brent W. Baccala" <cosine@freesoft.org> writes:

> Further progress trying to track this down:
> I don't have to shutdown the system to have problems.  "swapoff /dev/hd0s5"
> is enough to cause problems, once enough swap is in use.  After a failed
> swapoff, I have an extra 98 storeio processes running!


So we are seeing different problems.  I sometimes see the shutdown hang
way before swapoff is called.

Nevertheless, I have finished my little utility that you can use to make
a shell survive the shutdown process:


> I don't have to swapoff to have "symptoms".  The kernel debugger normally
> shows symbolic names, i.e:
> Stopped  at  machine_idle+0xe:   leave
> machine_idle(0,81a2c630,3806f64,0,9b448b38)+0xe
> idle_thread_continue(9fcbdde0,81028b50,9c0c7fe4,0,9c3d5548)+0x2a
> Once I've got enough swap in use, though, it stops doing this.  Now I see:
> Stopped       at  0x810000be: leave
> 0x810000be(0,0,9fcc5990,0,9fb90b30)
> 0x810293fa(9fcbdde0,81028b50,99526fe4,0,9c3d5548)

Uh :( that is not good.  That sounds like a swap-related corruption in
the kernel.

> When I see a kernel page fault, it's always in strcmp()

strcmp is used in the elf symbol lookup code, so that might explain the

> I can't task_terminate the auth server, as this typically does nothing once
> I've started having symptoms, but I can kill the auth server from the
> command line (just "kill 7") and that triggers a reboot that leaves the
> disk in a clean state.

Well, once the symbol lookup mechanism is fried, you likely cannot
!task_terminate anything anymore, since this relies on that mechanism.

> I'm just learning Hurd.  Any ideas?

Keep at it, the Hurd is an interesting system to learn from.  But you
might want to start with a simpler problem.


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