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On 2008-06-18T17:32:52+00:00 Bryce Harrington wrote:

Forwarding a Ubuntu bug:
https://bugs.edge.launchpad.net/ubuntu/+source/libxcb/+bug/232364

A number of Xubuntu users have been experiencing failures on startup
when launching dbus-launch.  Backtraces indicate the problem always
occurs during a select() call in _xcb_in_read_block.  The freezes are
intermittently reproducible (i.e., restart several times and eventually
it'll come up).

(gdb) bt
#0 0xb8002424 in __kernel_vsyscall ()
#1 0xb7e8484d in select () from /lib/tls/i686/cmov/libc.so.6
#2 0xb7da309a in _xcb_in_read_block (c=0x80579a8, buf=0x8057040, len=8)
    at xcb_in.c:248
#3 0xb7da2343 in xcb_connect_to_fd (fd=13, auth_info=0xbff1cdf0)
    at xcb_conn.c:133
#4 0xb7da4a51 in xcb_connect (displayname=0x0, screenp=0x0) at xcb_util.c:279
#5 0xb7f43717 in _XConnectXCB () from /usr/lib/libX11.so.6
#6 0xb7f2c029 in XOpenDisplay () from /usr/lib/libX11.so.6
#7 0x0804b3de in x11_init () at dbus-launch-x11.c:218
#8 0x0804abb2 in main (argc=5, argv=0xbff1d5a4) at dbus-launch.c:432
(gdb) quit

strace also shows that the hang is occurring on a select call:

  select(14, [13], NULL, NULL, NULL

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/23

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On 2008-06-18T17:35:41+00:00 Bryce Harrington wrote:

Some logs...
Xorg.0.log:  http://launchpadlibrarian.net/15420742/Xorg.0.log
xinitrc:  http://launchpadlibrarian.net/15420770/xinitrc
lsof:  http://launchpadlibrarian.net/15315169/lsof

This patch was attempted as a test, but found to make no difference:
http://launchpadlibrarian.net/14669590/xcb_in.diff

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/24

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On 2008-06-18T17:56:24+00:00 Cody A.W. Somerville wrote:

Hi,

 I'm the Xubuntu Team Lead. Please let me know if I can do anything to
assist in fixing/testing this bug.

Cheers,

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/25

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On 2008-06-20T15:00:13+00:00 Bryce Harrington wrote:

Created an attachment (id=17263)
dbus-launch trace

cody-somerville@mercurial:~$  cat /usr/bin/dbus-launch
#!/bin/sh

exec /usr/bin/strace /usr/bin/dbus-launch.real "$@" 2> /tmp/dbus-
launch.out

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/34

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On 2008-06-20T15:02:45+00:00 Bryce Harrington wrote:

Created an attachment (id=17264)
strace after killing process

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/35

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On 2008-06-20T15:03:13+00:00 Bryce Harrington wrote:

Created an attachment (id=17265)
lsof output

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/36

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On 2008-06-20T15:03:52+00:00 Bryce Harrington wrote:

Created an attachment (id=17266)
fd/pid listing

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/37

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On 2008-06-20T15:10:08+00:00 Bryce Harrington wrote:

>From the postkill:

[pid  7877] read(20, 0x8056f3c, 4096)   = -1 EAGAIN (Resource temporarily unavailable)
[pid  7877] ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbfd17a18) = -1 ENOTTY (Inappropriate ioctl for device)
[pid  7877] select(21, [20], NULL, [20], NULL) = 1 (in [20])
[pid  7877] read(20, "", 4096)          = 0

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/38

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On 2009-10-09T11:10:53+00:00 Jamey-minilop wrote:

I can't actually believe this was ever an XCB bug. The strace output
posted on the launchpad bug shows that it was waiting for the connection
setup response from the X server, and if that never arrived, it's hard
to imagine how it could be XCB's fault.

I could believe, though, that two instances of dbus-launch somehow
deadlocked against each other. Perhaps one calls XGrabServer, then waits
for the other one to finish connecting to the X server?

The fix that Ubuntu seems to have settled on, if I'm reading the
launchpad bug correctly, is to ensure that there aren't two dbus-launch
instances racing each other. That seems plausible to me.

Reply at: https://bugs.launchpad.net/dbus/+bug/232364/comments/76


** Changed in: libxcb
       Status: Invalid => Won't Fix

** Changed in: libxcb
   Importance: Unknown => Critical

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