[Bug runtime/13536] New: staprun -u race condition

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

http://sourceware.org/bugzilla/show_bug.cgi?id=13536

             Bug #: 13536
           Summary: staprun -u race condition
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap@sourceware.org
        ReportedBy: fche@redhat.com
    Classification: Unclassified


When staprun -u/PATH is used, staprun.c:enable_uprobes() first checks
if uprobes is already in the kernel (via a hacky grep on /proc/kallsyms;
see commit 14fe042), and if that fails, it tries to insert_module the
given bad boy.  This is racy, and can result in errors such as

Error inserting module '/tmp/staphDa9p3/uprobes/uprobes.ko': File exists
WARNING: /notnfs/INST/bin/staprun exited with status: 1
Pass 5: run failed.  Try again with another '--vp 00001' option.

It's better to try and fail, than to race.

Since bug #5163, $prefix/share/systemtap/runtime/uprobes/* is never
built, so actually staprun -u (without the /path) will not generally
work.  So testsuite/.../buildid.exp needs to be updated not to muck
with -u.

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