chiark / gitweb /
logind: save /run/systemd/users/UID before starting user@.service
Previously, this had a race condition during a user's first login.
Some component calls CreateSession (most likely by a PAM service
other than 'systemd-user' running pam_systemd), with the following
results:
- logind:
* create the user's XDG_RUNTIME_DIR
* tell pid 1 to create user-UID.slice
* tell pid 1 to start user@UID.service
Then these two processes race:
- logind:
* save information including XDG_RUNTIME_DIR to /run/systemd/users/UID
- the subprocess of pid 1 responsible for user@service:
* start a 'systemd-user' PAM session, which reads XDG_RUNTIME_DIR
and puts it in the environment
* run systemd --user, which requires XDG_RUNTIME_DIR in the
environment
If logind wins the race, which usually happens, everything is fine;
but if the subprocesses of pid 1 win the race, which can happen
under load, then systemd --user exits unsuccessfully.
To avoid this race, we have to write out /run/systemd/users/UID
even though the service has not "officially" started yet;
previously this did an early-return without saving anything.
Record its state as OPENING in this case.
Bug: https://github.com/systemd/systemd/issues/232
Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>