Is PTRACE_SINGLEBLOCK buggy?

[Jan Kratochvil]

On Mon, 02 Jun 2008 11:09:56 +0200, Renzo Davoli wrote:
> Jan Kratochvil has just sent me an E-mail saying that it seems to be 
> a kvm bug (or a bug caused by kvm).

KVM bug details at https://bugzilla.redhat.com/show_bug.cgi?id=437028 .

> He is right: using qemu/kqemu instead of kvm it does not panic.
> 
> Anyway I am puzzled. Using kvm the PTRACE_SINGLEBLOCK should have the
> same effect on 2.6.25.4 and 2.6.25.4+utrace.
> 2.6.25.4: ptrace_resume(kernel/ptrace.c)->user_enable_block_step
> 2.6.25.4+utrace: 
>  ptrace_common(kernel/ptrace.c) sets UTRACE_ACTION_BLOCKSTEP 
>  ->utrace_quiescent(kernel/utrace.c) tests UTRACE_ACTION_BLOCKSTEP 
>  ->user_enable_block_step
> I wonder where is the difference...

Just FYI on 2.6.25 I still get the crash,
  host: kernel: kvm: 19661: cpu0 unhandled wrmsr: 0x1d9 data 2
        kernel-2.6.25.3-18.fc9.x86_64
        kvm-65-7.fc9.x86_64
  guest: vanilla 2.6.25 x86_64
         Pid: 1945, comm: block-step Not tainted 2.6.25-0.101.rc4.git3.fc8 #1
         RIP: 0010:[<ffffffff8100ab79>]  [<ffffffff8100ab79>] __switch_to+0x218/0x2bc
         (the version number is for a RPM-built vanilla kernel)
(I did not find any ptrace patches in between 2.6.25 and 2.6.25.4.)


Regards,
Jan