In the change in commit 09a05394fe, I
overlooked two nits in the logic and this broke using CLONE_PTRACE
when PTRACE_O_TRACE* are not being used.
A parent that is itself traced at all but not using PTRACE_O_TRACE*,
using CLONE_PTRACE would have its new child fail to be traced.
A parent that is not itself traced at all that uses CLONE_PTRACE
(which should be a no-op in this case) would confuse the bookkeeping
and lead to a crash at exit time.
This restores the missing checks and fixes both failure modes.
Reported-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Roland McGrath <roland@redhat.com>
5861bbfcc1