Bug#963493: Repeatable hard lockup running strace testsuite on 4.19.98+ onwards

[Steve McIntyre <steve@einval.com>]

On Fri, Jun 26, 2020 at 10:29:28AM -0700, John Johansen wrote:
>On 6/26/20 9:50 AM, Steve McIntyre wrote:
>> 
>> OK, will try that second...
>> 
>
>I have not been able to reproduce but
>
>So looking at linux-4.19.y it looks like
>1f8266ff5884 apparmor: don't try to replace stale label in ptrace access check
>
>was picked without
>ca3fde5214e1 apparmor: don't try to replace stale label in ptraceme check
>
>Both of them are marked as
>Fixes: b2d09ae449ced ("apparmor: move ptrace checks to using labels")
>
>so I would expect them to be picked together.
>
>ptraceme is potentially updating the task's cred while the access check is
>running.
>
>Try building after picking
>ca3fde5214e1 apparmor: don't try to replace stale label in ptraceme check

Bingo! With that one change the test suite runs to completion, no lockup.

\o/

Thanks guys, I think we've found the cause here.

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
"The whole problem with the world is that fools and fanatics are
 always so certain of themselves, and wiser people so full of doubts."
   -- Bertrand Russell