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FreeBSD-EN-19:14.epoch Errata Notice
The FreeBSD Project
Topic: Incorrect locking in epoch(9)
Category: core
Module: kernel
Announced: 2019-08-06
Credits: Mark Johnston
Affects: FreeBSD 12.0
Corrected: 2019-07-27 16:11:04 UTC (stable/12, 12.0-STABLE)
2019-08-06 17:07:43 UTC (releng/12.0, 12.0-RELEASE-p9)
For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
.
I. Background
Some parts of the kernel use a new synchronization primitive, epoch(9),
which can be used to implement safe memory reclamation. In this usage,
threads can use the epoch(9) KPI to ensure that no other threads hold
a reference to a given object in memory.
II. Problem Description
In the case where epoch(9) must wait for a thread that is blocked on
a lock, it will use the turnstile(9) KPI to propagate the current
thread's priority to the lock holder. However, in the case where the
lock has no designated owner - for example, it is a reader-writer lock
owned by one or more readers - a bug in the interaction with the
turnstile meant that pair of spin locks were left locked when they
should have been unlocked.
III. Impact
In rare cases and under heavy load, the kernel may panic or lock up.
IV. Workaround
No workaround is available.
V. Solution
Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date, and reboot.
1) To update your system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for errata update"
2) To update your system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch https://security.FreeBSD.org/patches/EN-19:14/epoch.patch
# fetch https://security.FreeBSD.org/patches/EN-19:14/epoch.patch.asc
# gpg --verify epoch.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in
and reboot the
system.
VI. Correction details
The following list contains the correction revision numbers for each
affected branch.
Branch/path Revision
- -------------------------------------------------------------------------
stable/12/ r350373
releng/12.0/ r350641
- -------------------------------------------------------------------------
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
VII. References
The latest revision of this advisory is available at
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