[Bug 232364] [NEW] dbus-launch hangs at session start waiting on socket output in libxcb

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Cody A.W. Somerville (cody-somerville):

Ubuntu 8.04

It is not reproducible (I don't know when it happens). But it happens often enough.
dbus-launch can't be killed with SIGTERM (nor it dies when X session is killed, nor after
Ctrl-Alt-Backspace) when it happens and seem to hang on some synchronization
routine IIRC from the last time I tried to debug the issue.

I installed dbgsyms this times and will try to debug dbus-launch next
time it happens.

BTW, isn't dbus-launch supposed to exit after dbus-daemon is started
(for the user session)?

[Workaround]
kill the "dbus-launch --sh-syntax --exit-with-session" with signal 9.  This allows the login process to finish.

Or else just reboot several times.  It seems to be a race condition and
some people see it affecting login only intermittently.

[Background]
Due to various problems in the venerable xlib, Xorg upstream created the "X C-Language Bindings" (XCB).  Debian and Ubuntu switched to an xcb-enabled libx11 in the Hardy timeframe.  Prior to this, a known issue with Java (bug LP: #86103) prevented us from shipping XCB in Xorg.  A patch to enable 'sloppy locking' solved the java issue and allowed Ubuntu to follow Debian in shipping with this enabled in Hardy.

[Next Steps]
XCB is a new technology and as such is a prominent suspect, however we've not yet proven it as the culprit beyond a shadow of doubt.  A non-XCB libx11 package has been prepared for testing, and so the first step is to demonstrate conclusively that the issue is completely absent with that package.

Since Hardy is an LTS, it is important that we have this issue fixed,
however disabling XCB in libx11 maybe too short sighted; doing so could
just unpredictably generate regressions in other packages, and it really
only sweeps the problem under the rug for us to re-encounter later.
Much better would be to work with upstream to get this issue resolved
definitively.  Going forward, as more X client applications start
depending on XCB, having it available in Hardy will be of obvious
benefit.  But if we can show that a non-XCB libx11 resolves the issue,
and no other viable workaround or solution comes to light, we may have
no choice than to fall back to that.

** Affects: dbus
     Importance: Unknown
         Status: Fix Released

** Affects: libxcb
     Importance: Unknown
         Status: Confirmed

** Affects: dbus (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: libx11 (Ubuntu)
     Importance: Undecided
         Status: Invalid

** Affects: libxcb (Ubuntu)
     Importance: Critical
         Status: Triaged

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Invalid

** Affects: xfce4-session (Ubuntu)
     Importance: Undecided
         Status: Invalid

** Affects: xfce4-utils (Ubuntu)
     Importance: Critical
     Assignee: Cody A.W. Somerville (cody-somerville)
         Status: In Progress

** Affects: dbus (Ubuntu Hardy)
     Importance: Undecided
         Status: New

** Affects: libx11 (Ubuntu Hardy)
     Importance: Undecided
         Status: Invalid

** Affects: libxcb (Ubuntu Hardy)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu Hardy)
     Importance: Undecided
         Status: Invalid

** Affects: xfce4-session (Ubuntu Hardy)
     Importance: Undecided
         Status: Invalid

** Affects: xfce4-utils (Ubuntu Hardy)
     Importance: Critical
     Assignee: Cody A.W. Somerville (cody-somerville)
         Status: In Progress

-- 
dbus-launch hangs at session start waiting on socket output in libxcb
https://bugs.edge.launchpad.net/bugs/232364
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