unity8 crashed with SIGSEGV in QLightDM::GreeterImpl::authenticateWithPam() when logging in

StacktraceTop:
 _IO_vfprintf_internal (s=s@entry=0x7fb2ea5b69d0, format=<optimized out>, format@entry=0x7fb2f7a8f2d3 "%s(%s:%s):", ap=ap@entry=0x7fb2ea5b6b08) at vfprintf.c:2039
 __GI___vasprintf_chk (result_ptr=0x7fb2ea5b6be8, flags=1, format=0x7fb2f7a8f2d3 "%s(%s:%s):", args=args@entry=0x7fb2ea5b6b08) at vasprintf_chk.c:66
 __asprintf_chk (result_ptr=result_ptr@entry=0x7fb2ea5b6be8, flags=flags@entry=1, format=format@entry=0x7fb2f7a8f2d3 "%s(%s:%s):") at asprintf_chk.c:32
 asprintf (__fmt=0x7fb2f7a8f2d3 "%s(%s:%s):", __ptr=0x7fb2ea5b6be8) at /usr/include/x86_64-linux-gnu/bits/stdio2.h:178
 pam_vsyslog (pamh=0x2330710, priority=3, fmt=0x7fb2f7a8dc38 "application failed to re-exec stack [%d:%d]", args=args@entry=0x7fb2ea5b6c40) at pam_syslog.c:81

Full stacktrace, including u8 symbols (missing in the automatic retrace).

Unity seems fine actually, but crash happens when calling pam_authenticate where the pamHandle is something like:

{authtok = 0x7fb300000000 <error: Cannot access memory at address 0x7fb300000000>,
  caller_is = 3944807584, pam_conversation = 0xffffffff, oldauthtok = 0x0, prompt = 0x0,
  service_name = 0x0, user = 0x0, rhost = 0x0,
  ruser = 0xffffffff <error: Cannot access memory at address 0xffffffff>, tty = 0x0,
  xdisplay = 0x0, authtok_type = 0x0, data = 0x0, env = 0x0, fail_delay = {set = PAM_FALSE,
    delay = 0, begin = 0, delay_fn_ptr = 0x0}, xauth = {namelen = 0,
    name = 0xffffffffffffffff <error: Cannot access memory at address 0xffffffffffffffff>,
    datalen = 36901392,
    data = 0xffffffff00000001 <error: Cannot access memory at address 0xffffffff00000001>},
  handlers = {module = 0x232d370, modules_allocated = 36855568, modules_used = 0,
    handlers_loaded = 36898784, conf = {authenticate = 0x0, setcred = 0x21,
      acct_mgmt = 0x6d6f6e675f6d6170, open_session = 0x6e697279656b5f65,
      close_session = 0x7f006f730067, chauthtok = 0x21}, other = {
      authenticate = 0x6c61776b5f6d6170, setcred = 0x6f730074656c, acct_mgmt = 0x0,
      open_session = 0xd1, close_session = 0x7fb300000000, chauthtok = 0x0}}, former = {
    choice = -1, depth = 0, impression = 0, status = 0, substates = 0x0, fail_user = 0,
    want_user = 0, prompt = 0x0, update = PAM_FALSE},
  mod_name = 0xffffffff <error: Cannot access memory at address 0xffffffff>, mod_argc = 0,
  mod_argv = 0x0, choice = 0, audit_state = 0}

Not sure if it might be a threading issue

Yeah, seems to be a threading issue, I can reproduce by stress-testing rapidly asking our pam glue layer for logins. Working on it.

OK, I have a proposed fix: https://code.launchpad.net/~mterry/unity8/cancel-pam-harder/+merge/251174

When jenkins makes debs for that MP, could you try those debs and see if they help?

Sorry, I missed your ping on IRC (I was giving a talk about this stuff at that time :)), but yes: I've just downloaded latest vivid, installed the unity8 desktop on mir, unblacklisted the mesa drivers from virtualbox (to get 3d acceleration), and that's it.

I'll try the debs as soon as jenkins will build them (in case I miss that, please ping me)

Thanks

@Marco, the debs are there now

Cool, fix works here!

@Marco, thank you so much! I'll note that the fix has been tested in the MP.

untagging for vivid-stab-candidate, this code should be the same for rtm - and evidence seen
and this is only reproducible on vmware desktop (so not priority for mobile devices)

This bug was fixed in the package unity8 - 8.02+15.10.20150518.1-0ubuntu1

---------------
unity8 (8.02+15.10.20150518.1-0ubuntu1) wily; urgency=medium

  [ Albert Astals Cid ]
  * Add overrides to override functions
  * Implement "rating-edit" preview widget (LP: #1318144)
  * Make the DashContent::test_mainNavigation test more stable (LP:
    #1450809)
  * Use art height as implicitHeight when the header is overlayed and
    there's no summary

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk.

  [ Daniel d'Andrada ]
  * Introducing FloatingFlickable
  * Make Ubuntu.Gestures components install TouchRegistry by themselves

  [ Michael Terry ]
  * Fix a possible crash in our PAM threading code. (LP: #1425362) (LP:
    #1425362)
  * Fix the lockscreen becoming unresponsive after testing an app on the
    device from QtCreator. (LP: #1435364)

  [ Nick Dedekind ]
  * Fixed desktop stage app focus.
  * Fixed issue in laggy indicator autpilot tests (LP: #1446846)

 -- CI Train Bot <email address hidden> Mon, 18 May 2015 23:04:39 +0000

This bug was fixed in the package unity8 8.02+15.04.20150603.1-0ubuntu1 in https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/stable-phone-overlay

---------------

unity8 (8.02+15.04.20150603.1-0ubuntu1) vivid; urgency=medium

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk.

  [ Renato Araujo Oliveira Filho ]
  * Set the device led color to green. (LP: #1450894)

unity8 (8.02+15.10.20150518.1-0ubuntu1) wily; urgency=medium

  [ Albert Astals Cid ]
  * Add overrides to override functions
  * Implement "rating-edit" preview widget (LP: #1318144)
  * Make the DashContent::test_mainNavigation test more stable (LP:
    #1450809)
  * Use art height as implicitHeight when the header is overlayed and
    there's no summary

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk.

  [ Daniel d'Andrada ]
  * Introducing FloatingFlickable
  * Make Ubuntu.Gestures components install TouchRegistry by themselves

  [ Michael Terry ]
  * Fix a possible crash in our PAM threading code. (LP: #1425362) (LP:
    #1425362)
  * Fix the lockscreen becoming unresponsive after testing an app on the
    device from QtCreator. (LP: #1435364)

  [ Nick Dedekind ]
  * Fixed desktop stage app focus.
  * Fixed issue in laggy indicator autpilot tests (LP: #1446846)

unity8 (8.02+15.04.20150511-0ubuntu1) vivid; urgency=medium

  [ Albert Astals Cid ]
  * Workarounds for concierge mode.

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk.

unity8 (8.02+15.04.20150505-0ubuntu1) vivid; urgency=medium

  [ Albert Astals Cid ]
  * Make runtests fake a test error if make fails
  * Make the test more stable
  * Use dbus-test-runner instead of dbus-launch

  [ Daniel d'Andrada ]
  * DirectionalDragArea: improvements & API grooming (LP: #1417920)
  * Fix EdgeDragEvaluator when a drag can happen both ways
    (Direction.Horizontal)

  [ Josh Arenson ]
  * Remove panelHeight property as it is unused.

  [ Leo Arias ]
  * Initial clean up of the autopilot tests set up. Removed the touch
    device from the test case. Moved the restart of unity to a fixture.
    Removed the unused DragMixin. Updated the setUpClass to use
    process_helpers. Removed the workaround for bug #1238417, already
    fixed. Use the toolkit helper to set the testability environment
    variable. Fixed the indicators base class that was restarting unity
    twice. (LP: #1238417, #1447206)
  * Use the base class from the toolkit in autopilot tests.

  [ Michael Zanetti ]
  * emit application-stop when we're going down (LP: #1326513)

  [ Michał Sawicz ]
  * UNITY_SCOPES_LIST is no more

  [ handsome_feng<email address hidden> ]
  * When click the favorite scope in Dash Manager , it just return to
    the corresponding scope page. (LP: #1447056)

unity8 (8.02+15.04.20150422-0ubuntu1) vivid; urgency=medium

  [ Albert Astals Cid ]
  * Compile with Qt 5.5 (LP: #1437238)
  * Different way of top aligning labels when the other one in the row
    is multiline (LP: #1442085)
  * make pot_file

  [ Andrea Cimitan ]
  * Set sourceSize for DashBackground.qml Image

  [ CI Train Bot ]
  * New rebuild forced.
  * Resync trunk. added: po/sk.po

  [ Daniel d'Andrada ]
  * Move handling of comma...