[uml-devel] skas3-related crash of the week

[Nix <nix@esperi.org.uk>]

Using unmodified 2.4.22-6. sshed in through the firewall on the UML
instance, with tty logging enabled: typing exit on the last sshed-in
console froze the box yielded this on the console before UML died:

Kernel panic: switch_mm_skas - PTRACE_SWITCH_MM failed, errno = 9

Kernel panic: switch_mm_skas - PTRACE_SWITCH_MM failed, errno = 9

Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: switch_mm_skas - PTRACE_SWITCH_MM failed, errno = 9

Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Kernel mode fault at addr 0x4, ip 0x400e64ce
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
Kernel panic: Segfault with no mm
In idle task - not syncing
 <0>Kernel panic: Segfault with no mm
In idle task - not syncing

EBADF is a rather odd error to get from ptrace(): I wonder if this has
the same root cause as the EMFILE error I got a couple of weeks ago? It
looks like the error came from proc_mm_get_mm(), so something like
running out of fhs might explain it. Whatever it is, it's pretty
persistent: it looks like it panic-kills every process in turn until
it runs out.

As before, post-crash the box isn't remotely close to running out of
fhs:

1437    208     8192


(Now that the instance has crashed, I have an excuse to rebuild it with
debugging turned on, so the next report like this should have
backtraces.)

-- 
`Me, I want exploding spaceships and pulverized worlds and clashes of
 billion-year-old empires *and* competently written sentences.'
                                                    --- Matt Austern


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