Re: [PATCH v4 2/5] x86, traps: Track entry into and exit from IST context

[Andy Lutomirski <luto@amacapital.net>]

On Fri, Jan 23, 2015 at 10:04 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Jan 23, 2015 at 09:58:01AM -0800, Andy Lutomirski wrote:
>> > [  543.999079] Call Trace:
>> > [  543.999079] dump_stack (lib/dump_stack.c:52)
>> > [  543.999079] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4259)
>> > [  543.999079] atomic_notifier_call_chain (include/linux/rcupdate.h:892 kernel/notifier.c:182 kernel/notifier.c:193)
>> > [  543.999079] ? atomic_notifier_call_chain (kernel/notifier.c:192)
>> > [  543.999079] notify_die (kernel/notifier.c:538)
>> > [  543.999079] ? atomic_notifier_call_chain (kernel/notifier.c:538)
>> > [  543.999079] ? debug_smp_processor_id (lib/smp_processor_id.c:57)
>> > [  543.999079] do_debug (arch/x86/kernel/traps.c:652)
>> > [  543.999079] ? trace_hardirqs_on (kernel/locking/lockdep.c:2609)
>> > [  543.999079] ? do_int3 (arch/x86/kernel/traps.c:610)
>> > [  543.999079] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2554 kernel/locking/lockdep.c:2601)
>> > [  543.999079] debug (arch/x86/kernel/entry_64.S:1310)
>>
>> I don't know how to read this stack trace.  Are we in do_int3,
>> do_debug, or both?  I didn't change do_debug at all.
>
> It looks like we're in do_debug. do_int3 is only on the stack but not
> part of the current frame if I can trust the '?' ...
>

It's possible that an int3 happened and I did something wrong on
return that caused a subsequent do_debug to screw up, but I don't see
how my patch would have caused that.

Were there any earlier log messages?

--Andy