gnome-shell crashed with assertion failure "!xcb_xlib_threads_sequence_lost" [xcb_io.c:260]

Bug #1886059 reported by bug bridge on 2020-07-02

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This bug affects 2 people
Affects Status Importance Assigned to Milestone
gnome-shell (Ubuntu)
mutter (Ubuntu)
Daniel van Vugt

Bug Description

The Ubuntu Error Tracker has been receiving reports about a problem regarding gnome-shell. This problem was most recently seen with package version 3.36.3-1ubuntu2, the problem page at contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at

Similar error:

description: updated
Changed in gnome-shell (Ubuntu):
status: New → Incomplete
Changed in mutter (Ubuntu):
assignee: nobody → Daniel van Vugt (vanvugt)

Seems similar to that was supposed to be fixed, but not in all the cases, it seems.

Daniel van Vugt (vanvugt) wrote :
summary: - /usr/bin/gnome-shell:gnome-shell: ../../src/xcb_io.c:260:
- poll_for_event: F\303\266rs\303\244kran
- \342\200\235!xcb_xlib_threads_sequence_lost\342\200\235 falsk.
+ gnome-shell crashed with assertion failure
+ "!xcb_xlib_threads_sequence_lost" [xcb_io.c:260]
Changed in gnome-shell (Ubuntu):
status: Incomplete → Confirmed
Changed in mutter (Ubuntu):
status: New → Confirmed
Daniel van Vugt (vanvugt) wrote :

The stack trace is a little different. It will be interesting to see if we have anything like the same quantity of this crash as bug 1877075.

We should keep an eye on this to see if it is specific to some extension, or maybe to some specific graphics driver.

Not sure an extension can have a role here, as they can't do operations in other threads, being in JS.

But sure, so far we don't have enough data to identify the problem.

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I've just got a similar crash when just clicking on a menu item, I've got some more complete stacktrace, but don't think is really helpful

#0 __GI_raise (sig=<optimized out>) at ../sysdeps/unix/sysv/linux/raise.c:50
        set =
            {__val = {0, 548, 549, 550, 551, 552, 553, 554, 555, 556, 557, 558, 559, 15822592872050180864, 94249823962208, 94249845226528}}
        pid = <optimized out>
        tid = <optimized out>
#1 0x000055b83f47052a in ()
#2 0x00007f45908a3210 in <signal handler called> () at /lib/x86_64-linux-gnu/
#3 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
        set =
            {__val = {0, 139936754804816, 94252984795136, 94250118475456, 94250118475557, 94250118475456, 94250118475456, 94250118475568, 94250118475756, 94250118475456, 94250118475756, 0, 0, 0, 0, 0}}
        pid = <optimized out>
        tid = <optimized out>
#4 0x00007f4590882859 in __GI_abort () at abort.c:79
        save_stage = 1
        act =
          {__sigaction_handler = {sa_handler = 0x5, sa_sigaction = 0x5}, sa_mask = {__val = {112, 4, 48320015904, 0, 0, 139936755958789, 0, 21474836480, 140735042337344, 139936638613175, 139936638613175, 0, 15822592872050180864, 139936755958789, 139935137267712, 139936638613175}}, sa_flags = -1874503997, sa_restorer = 0x104}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#5 0x00007f4590882729 in __assert_fail_base
    (fmt=0x7f4589a2b6b7 <error: Cannot access memory at address 0x7f4589a2b6b7>, assertion=0x7f4590455858 "!xcb_xlib_threads_sequence_lost", file=0x7f45904556c3 "../../src/xcb_io.c", line=260, function=<optimized out>) at assert.c:92
        str = 0x55b850d16780 "\220ŻE\270U"
        total = 4096
#6 0x00007f4590893f36 in __GI___assert_fail
    (assertion=assertion@entry=0x7f4590455858 "!xcb_xlib_threads_sequence_lost", file=file@entry=0x7f45904556c3 "../../src/xcb_io.c", line=line@entry=260, function=function@entry=0x7f4590455b10 <__PRETTY_FUNCTION__.14999> "poll_for_event") at assert.c:101
#7 0x00007f45903e1493 in poll_for_event (dpy=dpy@entry=0x55b83fee4000, queued_only=queued_only@entry=0)
    at ../../src/xcb_io.c:260
        request = <optimized out>
        req = <optimized out>
        event = <optimized out>
        event_sequence = <optimized out>
        __PRETTY_FUNCTION__ = "poll_for_event"
#8 0x00007f45903e153d in poll_for_response (dpy=dpy@entry=0x55b83fee4000) at ../../src/xcb_io.c:278
        response = <optimized out>
        error = 0x55b83fee4000
        req = <optimized out>
        __PRETTY_FUNCTION__ = "poll_for_response"
#9 0x00007f45903e183a in _XEventsQueued (mode=<optimized out>, dpy=0x55b83fee4000)
    at ../../src/xcb_io.c:362
        response = <optimized out>
#10 _XEventsQueued (dpy=0x55b83fee4000, mode=<optimized out>) at ../../src/xcb_io.c:344
#11 0x00007f45903e482d in _XGetRequest
    (dpy=dpy@entry=0x55b83fee4000, type=type@entry=43 '+', len=len@entry=4) at ../../src/XlibInt.c:1764
        req = <optimized out>
--Type <RET> for more, q to quit, c to continue without paging--
#12 0x00007f45903dd62f in XSync (dpy=0x55b83fee4000, discard=discard@entry=0) at ../../src/Sync.c:43
        rep =
          {type = 48 '0', ...

Daniel van Vugt (vanvugt) wrote :

Yes that stack looks the same as before.

Daniel van Vugt (vanvugt) wrote :

Given that we've implemented the only known solution for this in bug 1877075, the remaining explanation for it might not be thread-related. Some kind of memory corruption (even single threaded) could have the same effect.

Dani (scrlk) wrote :

I don't know if this can help, but for me, the fail only happens after login and then I never see it again.

I just experienced this crash as well, but it was after being logged in for hours.

Daniel van Vugt (vanvugt) wrote :

I have an idea:

Anyone experiencing this crash reliably, please help us to find its root cause by editing your /etc/environment and adding a line:


and then reboot. Then next time a crash happens please tell us (here) the bug ID or error URL of the new crash.

Changed in gnome-shell (Ubuntu):
status: Confirmed → Incomplete
Changed in mutter (Ubuntu):
status: Confirmed → Incomplete
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