Description of problem:
Process SIGSTOPs, debugger PTRACE_ATTACHes it, first WAITPID(,,0) returns
SIGSTOP but second WAITPID(,,0) returns SIG_0 (that one should be waiting).

Version-Release number of selected component (if applicable):
FAIL:
F-8 kernel-2.6.25.9-40.fc8.i686
F-9 kernel-2.6.25.6-55.fc9.x86_64
F-9 kernel-2.6.25.9-76.fc9.x86_64
PASS:
kernel-vanilla-2.6.25.6-55.vanilla.fc9.x86_64
kernel-vanilla-2.6.25-0.101.rc4.git3.fc8.x86_64

How reproducible:
Always.

Steps to Reproduce:
wget -O stop-attach-then-wait.c
http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/stop-attach-then-wait.c?cvsroot=systemtap;
gcc -o stop-attach-then-wait stop-attach-then-wait.c -Wall -ggdb2 -D_GNU_SOURCE;
./stop-attach-then-wait; echo $?

Actual results:
1

Expected results:
0

Additional info:
Upstream bugreport post:
https://www.redhat.com/archives/utrace-devel/2008-June/msg00021.html