[Bug runtime/14659] New: task_finder2 breaks ptrace apps

["jistone at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14659

             Bug #: 14659
           Summary: task_finder2 breaks ptrace apps
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: jistone@redhat.com
    Classification: Unclassified


I'm running on kernel 3.5.4-1.fc17.x86_64, which is utrace-free, thus using
task_finder2.  I was trying to debug a problem between stapdyn and its module,
but when certain kernel-mode stap scripts are running, dyninst is completely
disrupted.  I can reproduce this with strace too, so I think it's a conflict
with ptrace().

First the good output, then the bad stap runs:

> $ strace -e read true
> read(4, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@\30B\273?\0\0\0"..., 832) = 832
> +++ exited with 0 +++


> $ stap -V
> Systemtap translator/driver (version 2.0/0.154, commit release-1.8-311-g44f25c1)
> Copyright (C) 2005-2012 Red Hat, Inc. and others
> This is free software; see the source for copying conditions.
> enabled features: AVAHI LIBRPM LIBSQLITE3 NSS BOOST_SHARED_PTR TR1_UNORDERED_MAP NLS DYNINST

> $ stap -e 'probe never{print_ubacktrace()}' -c 'strace -e read true'
> --- SIGTRAP {si_signo=SIGTRAP, si_code=0x5, si_pid=9294, si_uid=10719} ---
> --- SIGTRAP {si_signo=SIGTRAP, si_code=SI_KERNEL} ---
> +++ killed by SIGTRAP +++
> Warning: child process exited with signal 5 (Trace/breakpoint trap)
> WARNING: /usr/local/bin/staprun exited with status: 1
> Pass 5: run failed.  Try again with another '--vp 00001' option.

> $ stap -e 'probe process.begin{next}' -c 'strace -e read true'
> +++ exited with 0 +++

The same tests work fine on 2.6.32-279.5.2.el6.x86_64, with utrace, which is
why I blamed task_finder2 in the subject.  It could also be a bug in any of the
new kernel infrastructure that task_finder2 uses though.

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