[LTP] [PATCH] syscalls/ptrace07: handle potential SIGSEGV on older kernels

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> On Fri, Dec 21, 2018 at 9:51 PM Jan Stancek <jstancek@redhat.com> wrote:
> >
> > If a ptraced test process hits SIGSEGV, the entire testcase hangs.
> >
> > Older kernels such as RHEL7 (3.10.0), check the error code returned
> > by restore_fpu_checking() and do drop_init_fpu() if it fails.
> > So the FPU state of the prev task can't leak.
> >
> > But in the more likely case a task with xcomp_bv != 0 will be killed
> > by SIGSEGV; either from do_device_not_available() or from
> > sys_rt_sigreturn()->__restore_xstate_sig().
> >
> > And this is why the test case hangs; it wrongly assumes that the
> > traced child can only exit and report nothing else. But since it
> > receives SIGSEGV it reports this signal to the main process and
> > sleeps in ptrace_stop(), it does not exit and thus the test-case
> > hangs in tst_reap_children() after return from do_test().
> >
> > Replace PTRACE_CONT with PTRACE_DETACH, so we don't need to
> > handle subsequent stops. And treat exit code from test process
> > as info-only.
> 
> ptrace07(with this patch applied) passed with kernel 3.10 and 4.18
> multi arches test.
> 
> >
> > Debugged-by: Oleg Nesterov <onestero@redhat.com>
> > Signed-off-by: Jan Stancek <jstancek@redhat.com>
> 
> Tested-by: Li Wang <liwang@redhat.com>

Pushed.

Regards,
Jan