[Python-apps-team] Bug#959097: vdirsyncer: hang in FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME for some configs

[Bernhard Reiter]

Package: vdirsyncer
Version: 0.16.7-2
Severity: normal

Hi,
it is very nice that Debian packages vdirsyncer and thus helps
to maintain it. (As you may know, the original upstream author
is not happy about how this is handled, but also does not put much
time into vdirsyncer anymore. This makes the Debian packages even more
valuable in my eyes).


   * What led up to the situation?

When upgrading to Buster, I've switched using 
  vdirsyncer-latest [0.17.0a5~0+gac45bdc.d20180613]
from an external package source to the standard version with buster
There are three calendars configured, which are all just read_only
from a CALDAV source (all on the same server) to a singlefile .ics.

When trying a sync, vdirsyncer hangs on one calendar, the other two work.
  strace -p
on the process shows
futex(0x7f387429e890, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, FUTEX_BITSET_MATCH_ANY

   * What outcome did you expect instead?

A complete sync or an error message,
helping to diagnose the problem.



This is mainly for documenting the issue first,
to see if others run into the same issues.
Hints and potential solutions are appreciated, of course. :)
If time permitts, I'll do more analysis, possibly:
 * check if I can get https://wiki.python.org/moin/DebuggingWithGdb
   to get a better idea where it hangs in the application
 * try the 0.17. version with a manual install, to see if this is
   different (a short search on github did not reveal anything obviously
   related to this defect and 0.16.7 is the latest released version,
   even after 0.17a5.)
 * as it is read-only database, I may try to see, if it does away with
   fresh setup, though this may destroy the testable case.

Best Regards,
Bernhard

-- System Information:
Debian Release: 10.3
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-8-amd64 (SMP w/6 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8), LANGUAGE= (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages vdirsyncer depends on:
ii  python3                    3.7.3-1
ii  python3-atomicwrites       1.1.5-2
ii  python3-click              7.0-1
ii  python3-click-log          0.2.1-1
ii  python3-click-threading    0.4.4-1
ii  python3-requests           2.21.0-1
ii  python3-requests-toolbelt  0.8.0-1

vdirsyncer recommends no packages.

Versions of packages vdirsyncer suggests:
pn  python3-requests-oauthlib  <none>
ii  vdirsyncer-doc             0.16.7-2

-- no debconf information