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FreeBSD-EN-16:17.vm                                             Errata Notice
                                                          The FreeBSD Project

Topic:          Virtual Memory issues

Category:       core
Module:         Virtual Memory subsystem
Announced:      2016-10-25
Credits:        
Affects:        FreeBSD 10.3
Corrected:      2016-07-25 13:31:18 UTC (stable/10, 10.3-STABLE)
                2016-10-25 16:45:55 UTC (releng/10.3, 10.3-RELEASE-p11)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security branches,
and the following sections, please visit
<URL:https://security.freebsd.org/>.

I.   Background

The virtual memory subsystem manages address spaces of the processes, and
tightly cooperates with the file systems and process management to provide
the execution environment for the applications.

II.  Problem Description

Due to increased parallelism and optimizations in several parts of the
system, the previously latent bugs in VM become much easier to trigger,
affecting a significant number of the FreeBSD users.  The exact technical
details of the issues are provided in the commit messages of the merged
revisions, which are listed below with short summaries.

r301184 prevent parallel object collapses, fixes object lifecycle
r301436 do not leak the vm object lock, fixes overcommit disable
r302243 avoid the active object marking for vm.vmtotal sysctl, fixes
        "vodead" hangs
r302513 vm_fault() race with the vm_object_collapse(), fixes spurious
	SIGSEGV
r303291 postpone BO_DEAD, fixes panic on fast vnode reclaim

III. Impact

Due to the bugs, spurious SIGSEGV might be delivered to processes, causing
hangs on the "vodead" state on filesystem operations might be observed,
system might hang or panic during rapid UFS vnodes reclamation.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

2) To update your present 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

3) To update your present 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.

[FreeBSD 10.3]
# fetch https://security.FreeBSD.org/patches/EN-16:17/vm.patch
# fetch https://security.FreeBSD.org/patches/EN-16:17/vm.patch.asc
# gpg --verify vm.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
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r303291
releng/10.3/                                                      r307929
- -------------------------------------------------------------------------

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:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204764>

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204426>

The latest revision of this Errata Notice is available at
https://security.FreeBSD.org/advisories/FreeBSD-EN-16:17.vm.asc
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