[Bug 1447756] Proposed package removed from archive
martin.pitt at ubuntu.com
Thu May 12 13:48:00 UTC 2016
The version of upstart in the proposed pocket of Vivid that was
purported to fix this bug report has been removed because the bugs that
were to be fixed by the upload were not verified in a timely (105 days)
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[SRU] segfault in log.c code causes phone reboot loops
Status in Canonical System Image:
Status in upstart :
Status in upstart package in Ubuntu:
Status in upstart source package in Utopic:
Status in upstart source package in Vivid:
Status in upstart source package in Wily:
Status in upstart package in Ubuntu RTM:
= Summary =
The version of Upstart in vivid is affected by a coule of bugs relating
to the flushing data from early-boot jobs to disk which can both result
in a crash:
== Problem 1 ==
An internal list is mishandled meaning a crash could occur randomly.
== Problem 2 ==
Jobs which spawn processes in the background then themselves exit can
cause a crash due.
= Explanation of how Upstart flushes early job output =
If an Upstart job starts *and ends* early in the boot sequence (before
the log partition is mounted and writable) and produces output to its
stdout/stderr, Upstart will cache the output for later flushing by
adding the 'Log' object associated with the 'Job' to a list.
When the log partition is mounted writable, the
/etc/init/flush-early-job-log.conf job is run which calls "initctl
notify-disk-writeable". This is a signal to Upstart to flush its cache
of early-boot job output which takes the form of iterating the
'log_unflushed_files' list and flushing all the 'Log' entries to disk.
= Code Specifics =
There are 2 issues (note that the numbers used below match those used in
== Problem 1 detail ==
Due to a bug in the way the 'log_unflushed_files' list is handled (the
'Log' cannot be added to the list directly, so is added via an
intermediary ('NihListElem') node), a crash can result when iterating
the list since the 'Log' is freed, but NOT the intermediary node. The
implication is that it is possible for the intermediary node to be
attempt to dereference already-freed data, resulting in a crash.
== Problem 2 detail ==
If a job spawns a process in the background, then itself exits, that
jobs 'Log' entry will be added to the 'log_unflushed_files' list. But,
if the background process produces output and then exits before Upstart
attempts to flush the original jobs data to disk, the 'NihIo'
corresponding to the log will be serviced automatically and the data
flushed to disk. The problem comes when Upstart receives the
notification to flush the 'log_unflushed_files' list, since that list
now contains an entry which has already been freed (since all its data
has already been flushed). The result is an assertion failure.
= Fix =
== Problem 1 fix ==
Correct the 'log_unflushed_files' list handling by freeing the
'NihListElem' (which will automatically free the 'Log' object), not by
simply freeing the 'Log' object itself.
* Branch: lp:~jamesodhunt/ubuntu/vivid/upstart/bug-1447756/
* New Upstart test added to avoid regression?: Yes.
== Problem 2 fix ==
Correct the assumption that the only entries in the
'log_unflushed_files' list will always have data to flush by checking if
there is in fact any data to flush; if not, remove the entry from the
'log_unflushed_files' list since it has already been handled
automatically by the 'NihIo'.
* Branch: lp:~jamesodhunt/upstart/bug-1447756-the-actual-fix
* New Upstart test added to avoid regression?: Yes.
= Workarounds =
If a system is affected by this bug, it will be manifested by a crash
early in the boot sequence.
To overcome the issue, either:
a) Boot by adding "--no-log" to the kernel command-line.
b) Disable the flush-early-job-log job (assuming the machine is
bootable) by running the following:
$ echo manual | sudo tee -a /etc/init/flush-early-job-log.override
= Impact =
The issue has been present in Upstart since logging was introduced but
no known instances of crashes relating to these problems have been
reported prior to this bug being reported (which relates the the issue
being seen on a very small subset of specific Ubuntu Touch phone
hardware where Upstart is used as the system init daemon).
Note that vivid still uses Upstart for managing the graphical session,
but now uses systemd by default for the system init daemon. Since the session (Upstart) init does not even require
a flush-early-job-log, the exposure to both the bug and the updated fix codepath is extremely limited.
= Test Case =
This bug is extremely hard to surface so the approach is simply to
check that the internal list can be iterated correctly by:
1) Booting the system with upstart
(select the Upstart option from the grub menu or add "init=/sbin/upstart" to the kernel command-line).
2) Running the following on a system booted with Upstart:
$ for i in $(seq 17); do sudo start flush-early-job-log; done
= Regression Potential =
- As noted in Impact, the problems fixed by this version of Upstart have not been observed on server/desktop systems before.
- The fix is already in wily and no problems have been reported.
- See Impact.
= Original Description =
We recently started getting reprots from phone users that their
devices go into a reboot loop after changing the language or getting
an OTA upgrade (either of both end with a reboot of the phone)
after a bit of research we collected the log at
this shows a segfault of upstarts init binary in the log.c code:
[ 6.999083]init: log.c:819: Assertion failed in log_clear_unflushed: log->unflushed->len
[ 7.000279]init: Caught abort, core dumped
[ 7.467176]Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000600
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