[Bug 713237] Re: shutdown segv due to race w/ free_waiter threads

[Rolf Leggewie]

lucid has seen the end of its life and is no longer receiving any
updates. Marking the lucid task for this ticket as "Won't Fix".

** Changed in: multipath-tools (Ubuntu Lucid)
       Status: Triaged => Won't Fix

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https://bugs.launchpad.net/bugs/713237

Title:
  shutdown segv due to race w/ free_waiter threads

Status in multipath-tools package in Ubuntu:
  Fix Released
Status in multipath-tools source package in Lucid:
  Won't Fix
Status in multipath-tools source package in Maverick:
  Won't Fix

Bug description:
  Binary package hint: multipath-tools

  ==========================================
  SRU Justification:
  1. Impact: segv on multipathd shutdown
  2. How bug was addressed: a patch was cherrypicked from upstream which fixes this
  3. Minimal patch: see patch in attached bzr tree
  4. TEST CASE: stop multipathd.
  5. Regression potential: none, this patch was taken from upstream.
  ==========================================

  I received a coredump from a customer (running a lucid-based system).
  Analyzing the core from multipathd shows that we are crashing in waiter.c::free_waiter().

  void free_waiter (void *data)
  {
   struct event_thread *wp = (struct event_thread *)data;

   /*
    * indicate in mpp that the wp is already freed storage
    */
   lock(wp->vecs->lock);

   if (wp->mpp)
    /*
     * be careful, mpp may already be freed -- null if so
     */
    wp->mpp->waiter = NULL;
   else
    condlog(3, "free_waiter, mpp freed before wp=%p,", wp);

   unlock(wp->vecs->lock); <<< Crashing here

   if (wp->dmt)
    dm_task_destroy(wp->dmt);

   FREE(wp);
  }

  The lock is NULL:

  (gdb) print wp->vecs->lock
  $3 = (pthread_mutex_t *) 0x0

  This appears to be the upstream issue fixed here:
  http://git.kernel.org/gitweb.cgi?p=linux/storage/multipath-tools/.git;a=commitdiff;h=a403f57b991f3be7c7ea6250d95fad1554c9d6ca

  This fix is currently missing from all versions of multipath-tools in
  lucid->natty.

  (The original customer issue was filed in the private bug #712875.)

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