** Description changed:
[Impact]
Apt and dpkg implemented the Frontend Locking API and unattended-
upgrades needs to adopt it to not leave the packaging system unlocked
while passing control to python-apt and dpkg to perform package
installations and removals. Leaving the packaging system unlocked caused
many crashes of u-u when other tools took the lock and in the worse case
let other package management tools operate on dpkg's database breaking
systems.
The change takes advantage of python-apt's new API and keeps the
frontend lock during the run of u-u and unlocks only the inner locks for
committing changes.
[Test case]
Run strace unattended-upgrades to upgrade several packages and check
that lock-frontend is acquired at the beginning and not released until
the end (not reacquired repeatedly).
Unfixed u-u's output is like this:
# strace unattended-upgrade --verbose --dry-run 2>&1 | grep lock
openat(AT_FDCWD, "/var/run/unattended-upgrades.lock",
O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 4
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 93
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 5
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 6
...
Fixed u-u's output is like that:
# strace unattended-upgrade --dry-run --verbose 2>&1 | grep lock
openat(AT_FDCWD, "/var/run/unattended-upgrades.lock",
O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 4
openat(AT_FDCWD, "/var/lib/dpkg/lock-frontend", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 8
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 10
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 57
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 10
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 69
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 10
openat(AT_FDCWD, "/var/cache/apt/archives/lock", O_RDWR|O_CREAT|O_NOFOLLOW,
0640) = 70
openat(AT_FDCWD, "/var/lib/dpkg/lock", O_RDWR|O_CREAT|O_NOFOLLOW, 0640) = 10
...
[Regression potential]
Incorrect lock API usage can make unattended-upgrades to crash, but it
is unlikely to hang since the lock handling operations are non-blocking.
Failing to reserve the locks can also cause problems by allowing other
package management tools to install packages in parallel, but this
problem existed in the past, too.
[Additional Info]
- Frontend lock support for apt and dpkg is tracked in LP: #1781169, this bug
tracks unattended-upgrades changes
+ This is part of a wider series of changes 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
** Also affects: unattended-upgrades (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: unattended-upgrades (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: unattended-upgrades (Ubuntu Bionic)
Status: New => In Progress
** Changed in: unattended-upgrades (Ubuntu Xenial)
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/1789637
Title:
Proper support for frontend lock
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