Description of problem:

When tracing multithreaded programs using ptrace on a Fedora kernel, I get
strange 0 signals instead of PTRACE_EVENT_EXIT events to traced threads when
they exit.

I have attached a test case that traces a process with two threads that just
exit and prints the events that ptrace reports.

If you compile the test case with "gcc -lpthread -o ptrace-bug ptrace-bug.c"
and run it on a vanilla 2.6.21.3 kernel, you get the expected messages (here
with manual annotations):

tid 25582: signal 19, ptrace event 0     SIGSTOP to parent from PTRACE_ATTACH
tid 25582: signal 5, ptrace event 3      SIGTRAP|PTRACE_EVENT_CLONE to parent
tid 25582: signal 5, ptrace event 6      SIGTRAP|PTRACE_EVENT_EXIT to parent
tid 25583: signal 19, ptrace event 0     SIGSTOP to child when created
tid 25583: signal 5, ptrace event 6      SIGTRAP|PTRACE_EVENT_EXIT to child
tid 25583: exit status 0                 Exit status from child
tid 25582: exit status 0                 Exit status from parent

If you run the test case on the Fedora kernel the PTRACE_EVENT_EXIT for the
second thread to exit is replaced by a signal 0:

tid 3026: signal 19, ptrace event 0
tid 3026: signal 5, ptrace event 3
tid 3026: signal 5, ptrace event 6
tid 3027: signal 19, ptrace event 0
tid 3027: signal 0, ptrace event 0       Signal 0???
tid 3027: exit status 0
tid 3026: exit status 0

Version-Release number of selected component (if applicable):

2.6.21-1.3194.fc7

How reproducible:

Every time.

Steps to Reproduce:

1. Compile and run the attached test case.

Actual results:

Signal 0 when second thread exits.

Expected results:

Same ptrace events as vanilla kernel.

Additional info: