[Bug translator/11151] New: Leakage of stap_uprobes slots

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

Systemtap generated module has a finite number of slots to store entries for
userspace probes. These slots are not reclaimined when a probed process exits.
Given enough runs of an process that is probed the systemtap script will fail
because the systemtap generated module has run out of slots. This will make it
difficult to have long running scripts to monitor long term system performance.

The generated module has the following data structure store information about
userspace probes:

#ifndef MAXUPROBES
#define MAXUPROBES 572
#endif
static struct stap_uprobe {
  union { struct uprobe up; struct uretprobe urp; };
  int spec_index;
  unsigned long sdt_sem_address;
} stap_uprobes [MAXUPROBES];

A simple example to demonstrate the problem was contructed using a very simple
systemtap script and a bash script to run the instrumented python available at:

http://people.redhat.com/wcohen/fudcon2009/

1) install the instrumented python rpms
2) run the systemtap script with:

   stap -v  /home/wcohen/research/profiling/pytrace2.stp

3) Start the pyloop.sh script

Expected result is the systemtap script will continue to run for
repeated runs of pyloop.sh, but the actual behavior of the systemtap
script is:

ERROR: Skipped too many probes, check MAXSKIPPED or try again with stap -t for
more details.
WARNING: Number of errors: 0, skipped probes: 102
Pass 5: run completed in 10usr/70sys/22792real ms.

-- 
           Summary: Leakage of stap_uprobes slots
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: wcohen at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=11151

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