packagekit frontend locking

Bug #1795614 reported by Julian Andres Klode on 2018-10-02
10
This bug affects 1 person
Affects Status Importance Assigned to Milestone
packagekit (Ubuntu)
Status tracked in Cosmic
Xenial
Undecided
Unassigned
Bionic
Undecided
Unassigned
Cosmic
Undecided
Unassigned

Bug Description

[SRU Notes]

[rbasak] Requires apt 1.2.28 (Xenial) and 1.6.5 (Bionic), both of which are currently in proposed. Do not release to updates without releasing the newer apt first.

[Impact]
PackageKit needs an adjustment for frontend locking, so it does not release the frontend lock during dpkg invocations, but only the normal dpkg lock.

Frontend locking prevents race conditions between multiple dpkg frontends, which can cause other frontends to be interrupted while they are installing stuff - the frontend loses the dpkg lock between dpkg runs and the system ends up in a partially configured state.

See bug 1781169 for more details on frontend locking.

[Test case]
1. Install a package
2. Modify prerm to sleep
3. Remove package via pkcon and check that packagekitd process holds lock-frontend and dpkg holds lock (we release lock by closing the lock files, so just check if the files are open).

[Regression potential]
Changing the code to call UnLockInner() vs UnLock() makes it do less steps and only release "lock" as before, and not "lock-frontend". That should not be causing any regressions.

The patch also adds a call to LockInner() after the dpkg execution to make it reacquire "lock", this could fail. It should not have much impact however, as it only affects a single transaction AFAICT. It does reduce the risk of some frontend not implementing frontend locking from racing while we still hold the frontend lock, though.

[Other info]
This is part of a wider series of SRUs for frontend locking

- dpkg (bug 1796081)
- apt (bug 1781169)
- python-apt (bug 1795407)
- packagekit (bug 1795614)
- unattended-upgrades (bug 1789637)
- aptdaemon (no bug filed yet)

Further details about frontend locking can be found in https://lists.debian.org/debian-dpkg/2017/01/msg00044.html

Changed in packagekit (Ubuntu Cosmic):
status: New → Fix Released
Changed in packagekit (Ubuntu Bionic):
status: New → Triaged
Changed in packagekit (Ubuntu Xenial):
status: New → Triaged
description: updated
tags: added: id-5bae2d4a668b6f3b803fb88b
description: updated
Robie Basak (racb) wrote :

The updated description explains why frontend locking is necessary, but how does this particular bug impact users? What's wrong for users as a consequence of this bug? Eg. what user story is broken? I need to understand this in order to judge whether an SRU is warranted, which I'm supposed to consider as part of my SRU review.

description: updated
description: updated
Julian Andres Klode (juliank) wrote :

Added some more details, but I'm really at a loss what else you could want to know than it screwing up installations.

Balint Reczey (rbalint) wrote :

@rbasak If unattended-upgrades runs at the same time as software updater is updating apt caches then unattended upgrades crashes.

description: updated
description: updated
Robie Basak (racb) on 2018-10-04
description: updated

Hello Julian, or anyone else affected,

Accepted packagekit into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/packagekit/1.1.9-1ubuntu2.18.04.2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Changed in packagekit (Ubuntu Bionic):
status: Triaged → Fix Committed
tags: added: verification-needed verification-needed-bionic
Changed in packagekit (Ubuntu Xenial):
status: Triaged → Fix Committed
tags: added: verification-needed-xenial
Robie Basak (racb) wrote :

Hello Julian, or anyone else affected,

Accepted packagekit into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/packagekit/0.8.17-4ubuntu6~gcc5.4ubuntu1.4 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

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