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Security updates have been issued by Debian (cups-filters, dhcpcd5, faad2, ghostscript, graphicsmagick, jruby, lemonldap-ng, and libspring-security-2.0-java), Fedora (gnome-desktop3, java-1.8.0-openjdk-aarch32, libu2f-host, samba, sqlite, webkit2gtk3, xen, and ytnef), Mageia (docker, flash-player-plugin, freeradius, libsndfile, libxslt, mariadb, netpbm, python-jinja2, tomcat-native, and virtualbox), openSUSE (kernel and ucode-intel), and SUSE (kernel, kvm, libvirt, nmap, and transfig).

Wired looksat the security issues stemming from the complexity of the Bluetoothstandard. "Bluetooth has certainly been investigated to a degree, butresearchers say that the lack of intense scrutiny historically stems againfrom just how involved it is to even read the standard, much lessunderstand how it works and all the possible implementations. On the plusside, this has created a sort of security through obscurity, in whichattackers have also found it easier to develop attacks against otherprotocols and systems rather than taking the time to work out how to messwith Bluetooth."

Linus has released the 5.2-rc1 kernelprepatch and closed the merge window for this development cycle."Nothing particularly odd going on this merge window. I had sometravel in the middle of it, but to offset that I had a new fastertest-build setup, and most of the pull requests came in early (thank you)so my travels didn't actually end up affecting the merge window all thatmuch."

The ever-increasing complexity of the software stacks we work with has giventesting an important role. There was a recent intersection between theautomated testing being done by the Yocto Project (YP) and a bug introduced into the Linux kernel that gives some insight into what thefuture holds and the potential available with this kind of testing.

Six new stable kernels have been released: 5.1.3, 5.0.17,4.19.44, 4.14.120, 4.9.177, and 4.4.180. As usual, they contain importantfixes throughout the kernel tree; users should upgrade.

Security updates have been issued by Debian (jquery), Fedora (kernel-headers, php-typo3-phar-stream-wrapper, and python3), openSUSE (qemu, ucode-intel, and xen), Red Hat (chromium-browser, java-1.8.0-ibm, and rh-python35-python-jinja2), SUSE (containerd, docker, docker-runc, go, go1.11, go1.12, golang-github-docker-libnetwork, evolution, graphviz, kernel, qemu, and systemd), and Ubuntu (libmediainfo, libvirt, and Wireshark).

Over the past four years, LWN has covered the PythonLanguage Summit, but this year the Python Software Foundation (PSF) electedto go in a different direction, with coverage by A. Jesse Jiryu Davis onthe PSF blog. Those reports are being gathered on a summitpage; as of this writing there are two reports up with plenty more tocome. "The Python Language Summit is a small gathering of Pythonlanguage implementers, both the core developers of CPython and alternativePythons, held on the first day of PyCon. The summit features shortpresentations from Python developers and community members, followed bylonger discussions. The 2019 summit is the first held since Guido vanRossum stepped down as Benevolent Dictator for Life, replaced by afive-member Steering Council."

Even with radiators and fans, a system's CPUs can overheat. When thathappens, the kernel's thermal governor will cap the maximum frequency ofthat CPU to allow it to cool. The scheduler, however, is not aware that the CPU'scapacity has changed; it may schedule more work than optimal in the currentconditions, leading to a performance degradation. Recently, TharaGopinath didsome research and posted a patch set to address this problem. Thesolution adds an interface to inform the scheduler about thermal events sothat it can assign tasks better and thus improve the overall systemperformance.

Greg Kroah-Hartman has announced the release of the 3.18.140 stable kernel. "Note, this is the LAST 3.18.y release that I will be doing onkernel.org. I know it has been marked as End-of-Life for quite sometime, but I have kept it alive due to a few million phones out there inthe wild that depend on it, and can not move to a new kernel base due tothem being stuck with a SoC vendor that does not work upstream.But, this does not mean the tree is dead, oh no, if only it were thateasy..." He and others will be updating the kernel in the AndroidOpen Source Project (AOSP) tree.

Security updates have been issued by CentOS (freeradius, kernel, libvirt, and qemu-kvm), Debian (intel-microcode, linux-4.9, and samba), Fedora (kernel, kernel-headers, memcached, microcode_ctl, php-pecl-imagick, and samba), Mageia (kernel, kernel-linus, kernel-tmb, and microcode), openSUSE (389-ds, bzip2, jakarta-commons-fileupload, kernel, and pacemaker), Red Hat (flash-plugin and ruby), Scientific Linux (kernel, libvirt, qemu-kvm, and ruby), Slackware (rdesktop), and Ubuntu (libvirt).

The LWN.net Weekly Edition for May 16, 2019 is available.

Over the past year, Python has moved on from the benevolent dictator forlife (BDFL) governance model since Guido van Rossum steppeddown from that role. In February, a new steering council was elected based onthe governance model that was adopted inDecember. At PyCon 2019 inCleveland, Ohio, the five members of the steering council took the stage for akeynote panel that was moderated by Python Software Foundation (PSF)executive director Ewa Jodlowska.

We contemplated putting together an LWN article on the "microarchitecturaldata sampling" (MDS) vulnerabilities, as we've done for pastspeculative-execution issues. But the truth of the matter is that it'sreally more of the same, and there is a lot of material out there on thenet already. So, for those who would like to learn more, here's a list ofresources.

<p>Amir Goldstein led a discussion on things that the two major networkfilesystems for Linux, Samba and NFS, could cooperate on at the end of dayone of the 2019 Linux Storage, Filesystem, and Memory-Management Summit. Inparticular, are there needs that both filesystems have that the kernel isnot currently providing? He had some ideas of areas that might be tackled,but was looking for feedback from the assembled filesystem developers.

Michael Crosby is one of the most influential developers working on Dockercontainers today, helping to lead development of containerd as well as serving as the Open Container Initiative (OCI)Technical Oversight Chair. At DockerCon 19, Crosby led astanding-room-only session, outlining the past, present and — moreimportantly — the future of Docker as a container technology. The earlyhistory of Docker is closely tied with Linux and, as it turns out, so too isDocker's future.

Security updates have been issued by Debian (drupal7, intel-microcode, kernel, and lemonldap-ng), Red Hat (kernel, kernel-rt, libvirt, qemu-kvm, qemu-kvm-rhev, redhat-virtualization-host, rhvm-appliance, vdsm, virt:rhel, and wget), Scientific Linux (wget), SUSE (containerd, docker, docker-runc, go, go1.11, go1.12, golang-github-docker-libnetwork, kernel, libxslt, microcode_ctl, qemu, ucode-intel, and xen), and Ubuntu (intel-microcode, kernel, linux, linux-aws, linux-azure, linux-gcp, linux-kvm, linux-raspi2, linux, linux-aws, linux-kvm, linux-raspi2, linux-snapdragon, linux-hwe, linux-azure, linux-hwe, linux-azure, linux-gcp, linux-oracle, linux-lts-trusty, linux-lts-xenial, linux-raspi2, linux-snapdragon, qemu, and samba).

Here's a blog post from"Brent" on how PHP deserves another look. "Today I want to look at the bright side: let's focus on the things that have changed and ways to write clean and maintainable PHP code. I want to ask you to set aside any prejudice for just a few minutes.Afterwards you're free to think exactly the same about PHP as you did before. Though chances are you will be surprised by some of the improvements made to PHP in the last few years."

A new filesystem aimed at sharing host filesystems with KVM guests, virtio-fs, was the topic of a session led by Miklos Szeredi at the 2019 Linux Storage,Filesystem, and Memory-Management Summit. The existing solution, which isbased on the 9P filesystem from Plan 9, has someshortcomings, he said. Virtio-fs is a prototype that uses the Filesystem inUserspace (FUSE) interface.

This round of kernel updates address a speculative-execution vulnerability foundin all Intel processors made since 2011. Greg Kroah-Hartman says in the 5.1.2 kernel patch: "Note, this release,and the other stable releases that are all being released right now at thesame time, just went out all contain patches that have only seen the"public eye" for about 5 minutes. So be forwarned, they might breakthings, they might not build, but hopefully they fix things. Odds are wewill be fixing a number of small things in this area for the next few weeksas things shake out on real hardware and workloads." In addition to5.1.2, stable kernels 5.0.16, 4.19.43, 4.14.119, and 4.9.176 are available. More information may befound in the Xensecurity advisory and this new in-kerneldocumentation.

The curtain has finally been lifted on the latest set ofspeculative-execution vulnerabilities. This one has the delightful name ofZombieLoad; it is also known as"microarchitectural data sampling", but what's the fun in that? Various x86processors stash data into hidden buffers that can, in some cases, berevealed via speculative execution. Exploits appear to be relativelyhard. See this pagefrom the kernel documentation for a fairly detailed description of theproblem, and thispage for mitigation information.

The fifthand final article in Adrian Ratiu's serieson eBPF delves into userspace tracing. "In our previous parts we focused on tracing the Linux kernel, for which the eBPF-based projects are, in our humble opinion, the most safe, widely available and useful methods (eBPF is fully upstreamed in Linux, guarantees a stable ABI, comes enabled by default in almost all distributions and integrates with all other tracing mechanisms). It has really become a no-brainer choice for kernel work. However, up until now, talking in-depth about userspace tracing was deliberately avoided because it merits special treatment, hence this full part 5 article devoted to it."

The planning process for the 2019 Linux Kernel and Maintainer's Summits(Lisbon, Portugal, September 9 to 12) hasbegun. If you have a topic that you would like to see discussed at eitherevent, now is the time to send in a proposal to theksummit-discuss list; click below for the details.

<p>Trond Myklebust and Bruce Fields led a session on some topics of interestin the NFS world at the 2019 Linux Storage, Filesystem, andMemory-Management Summit. Myklebust discussed the intersection of NFS andcontainers, as well adding TLS support to NFS. Fields also had somecontainer changes to discuss, along with a grab bag of other areas thatneed attention.

Security updates have been issued by CentOS (flatpak, ghostscript, and python-jinja2), Debian (cups-filters, imagemagick, qt4-x11, and samba), Fedora (httpd and wpa_supplicant), openSUSE (freeradius-server, nmap, python-Jinja2, signing-party, and webkit2gtk3), Red Hat (java-1.7.1-ibm and java-1.8.0-ibm), Scientific Linux (python-jinja2), SUSE (cf-cli, java-1_8_0-openjdk, and libxslt), and Ubuntu (isc-dhcp, openjdk-8, openjdk-lts, samba, and VCFtools).

<p>In the filesystems track at the 2019 Linux Storage, Filesystem, andMemory-Management Summit, Ted Ts'o led a discussion about an inode flag toindicate DAX files, which is meant to be applied to files that should bedirectly accessed without going through the page cache. XFS has such aflag, but ext4 and other filesystems do not. The semantics of what the flag would mean arenot clear to Ts'o (and probably others), so the intent of the discussionwas to try to nail those down.

Security updates have been issued by Debian (atftp, ghostscript, openjdk-7, and postgresql-9.4), Fedora (java-11-openjdk, mosquitto, and php), Mageia (bash, binutils, clamav, cronie, jasper, kernel, mxml, openexr, openssh, python, qt4, svgsalamander, sysstat, tar, and tcpreplay), openSUSE (openssl, python3, sqlite3, webkit2gtk3, and wireshark), Red Hat (bind, flatpak, freeradius:3.0, java-1.8.0-openjdk, python-jinja2, rh-ror42-rubygem-actionpack, rh-ror50-rubygem-actionpack, rh-ruby23-ruby, rh-ruby24-ruby, rh-ruby25-ruby, and thunderbird), SUSE (389-ds, bzip2, ImageMagick, jakarta-commons-fileupload, java-1_8_0-openjdk, pacemaker, python-Django1, samba, and sqlite3), and Ubuntu (postgresql-10, postgresql-11, postgresql-9.5).

The latest set of stable kernel updates consists of5.1.1,5.0.15,4.19.42,4.14.118, and4.9.175.Each contains the usual set of important fixes.

When he released the 5.1 kernel, LinusTorvalds noted that he had a family event happening in the middle of the5.2 merge window and that he would be offline for a few days in the middle.He appears to be trying to make up for lost time before it happens: over8,300 non-merge changesets have found their way into the mainline in thefirst four days. As always, there is a widevariety of work happening all over the kernel tree.

Security updates have been issued by Debian (bind9, postgresql-9.6, qemu, and symfony), Fedora (kernel, kernel-tools, mod_cluster, rubygem-actioncable, rubygem-actionmailer, rubygem-actionpack, rubygem-actionview, rubygem-activejob, rubygem-activemodel, rubygem-activerecord, rubygem-activestorage, rubygem-activesupport, rubygem-rails, and rubygem-railties), openSUSE (wireshark), Red Hat (freeradius), Scientific Linux (freeradius), and Ubuntu (bind9 and wpa).

Eric Rescorla has written adetailed summary of how the Firefox add-on fiasco happened, how it wasaddressed, and how a repeat might be avoided. "First, we should havea much better way of tracking the status of everything in Firefox that is apotential time bomb and making sure that we don’t find ourselves in asituation where one goes off unexpectedly. We’re still working out thedetails here, but at minimum we need to inventory everything of thisnature."

The 2019 Linux Storage, Filesystem, and Memory-Management Summit differedsomewhat from its predecessors in that it contained a fourth trackdedicated to the BPF virtual machine. LWN was unable to attend most ofthose sessions, but a couple of BPF-related talks were a part of thebroader program. Among those was a plenary talk by Dave Miller, describedas "a wholistic view" of why BPF is successful, its current state, andwhere things are going.

Security updates have been issued by Fedora (drupal7, exiv2, filezilla, and libfilezilla), openSUSE (gnutls, GraphicsMagick, hostinfo, supportutils, and ovmf), Scientific Linux (flatpak and ghostscript), SUSE (mutt and samba), and Ubuntu (Monit).

The LWN.net Weekly Edition for May 9, 2019 is available.

<p>The idea of "inheritance" is something that most students learn about earlyon when they are studying object-oriented programming (OOP). But one ofthe seminal books about OOP recommends favoring "composition" overinheritance. Ariel Ortiz came to PyCon in Cleveland, Ohio to describe the composition pattern and to explain the tradeoffs between usingit and inheritance.

Computer memory architecture is growing more complex over time, withdifferent types of memory attached to a CPU via a number of paths. Thekernel development community is duly working to make this memory availableto user space in an equally diverse set of ways. Two sessions at the 2019Linux Storage, Filesystem, and Memory-Management Summit presented possiblemechanisms and APIs to allow programs to work with the types of memory theyneed.

Christoph Lameter has spent years improving Linux for high-performancecomputing tasks. During the memory-management track of the 2019 LinuxStorage, Filesystem, and Memory-Management Summit, he talked about theproblem of keeping up with a 400Gb/s network interface. At that speed,there simply is no time for the system to get its work done. Some ways ofimproving the situation are in sight, but it's a hard problem overall and,despite some progress, the situation is getting worse.

The mmap_sem lock used in the memory-management subsystem has beena known scalability problem for years, but it has proved difficult toremove. During a session in the memory-management track of the 2019 LinuxStorage, Filesystem, and Memory-Management Summit, Laurent Dufour andMatthew Wilcox discussed a possible solution: replacing the red-black treecurrently used to track virtual memory areas (VMAs) with a new datastructure called a "maple tree".

For years, kernel developers have been told to avoid allocating large chunks ofphysically contiguous memory; as the system runs and memory becomesfragmented, satisfying such allocations becomes increasingly difficult.But, as Zi Yan pointed out in a memory-management track session at the 2019Linux Storage, Filesystem, and Memory-Management Summit, there are timeswhen contiguous memory is useful. In this session, the memory-managementdevelopers discussed ways to make such allocations more likely to succeed.

kmalloc() is one of the kernel's fundamental memory-allocationprimitives for relatively small objects. Most of the time, developersdon't worry about the alignment of memory returned fromkmalloc(), and things generally just work. But, Vlastimil Babkasaid during a plenary session at the 2019 Linux Storage,Filesystem, and Memory-Management Summit, every now and thenkmalloc() will do something surprising. He proposed tighteningthe guarantees around object alignment in the hope of generating fewersurprises in the future.

At the 2018 Linux Storage, Filesystem, and Memory-Management Summit(LSFMM), Boaz Harrosh introduced the ZUFSfilesystem. At this year's event, he was back to talk about what itwould take to merge ZUFS into the mainline. ZUFS, which Harrosh pronouncedas both "zoo-eff-ess"and "zoofs", has been running in production for his employer's (NetApp's) customers for some time now, so he wondered if it was something that couldgo upstream.

Stable kernels 5.0.14, 4.19.41, 4.14.117, and 4.9.174 have been released. As usual there areimportant fixes and users should upgrade.

Security updates have been issued by Arch Linux (dovecot, kernel, linux-zen, munin, nautilus, perl-email-address, and tcpreplay), Debian (atftp), Fedora (perl-YAML and teeworlds), Mageia (java-1.8.0-openjdk, ldb, libsolv, and putty/filezilla/wxgtk), openSUSE (freeradius-server, libjpeg-turbo, pacemaker, rubygem-actionpack-5_1, wpa_supplicant, and yubico-piv-tool), Red Hat (chromium-browser, container-tools:rhel8, edk2, firefox, flatpak, ghostscript, httpd:2.4, mod_auth_mellon, openwsman, python-jinja2, python27:2.7, python3, python36:3.6, redhat-virtualization-host, systemd, and wget), SUSE (freeradius-server), and Ubuntu (ghostscript and wpa).

One fixture of the memory-management track at the Linux Storage,Filesystem, and Memory-Management Summit is a discussion with subsystemmaintainer Andrew Mortonon how the development process is going. The 2019 version indicated thatthe memory-management developers are mostly happy with how the process isworking, but there are still things that they would like to see changed. Whilesome of the issues are old and intractable, others may be amenable toshort-term improvement.

The problems associated with the kernel's internal get_user_pages()function have been a topic of discussion at the Linux Storage, Filesystem,and Memory-Management Summit for a few years. At the 2019 event, Jan Kara began a plenary session by saying that it would be "like lastyear's session". It turned out rather differently, though, perhaps due tothe plenary setting; this discussion (along with the related session thatfollowed) turned out to be one of the most heated at the entire conference.

Red Hat has announced therelease of Red Hat Enterprise Linux 8. "Modern IT is hybridIT. But turning a sprawling ecosystem—from traditional datacenters topublic cloud services—into a true hybrid environment requires a fewthings. Scaling as needed. Moving workloads seamlessly. Developing andmanaging applications that run anywhere. There's an operating system thatmakes those things possible. And now it gives you predictive analytics andremediation." See the releasenotes for more information.

Memory control groups exist to track and limit the amount of memory used bysets of processes. Normally, one would not expect that memory used by onegroup would be charged to another but, as Shakeel Butt described in amemory-management track session at the 2019 Linux Storage, Filesystem, andMemory-Management Summit, that does happen in a number of differentsituations. It's often a problem, but occasionally it's also a usefulfeature.

Security updates have been issued by Debian (389-ds-base, firefox-esr, and symfony), Fedora (poppler), SUSE (audit, ovmf, and webkit2gtk3), and Ubuntu (aria2, FFmpeg, gnome-shell, and sudo).

Control groups are a useful mechanism for managing resource usage in thesystem, but what happens when the control groups themselves become aresource problem? In a plenary session at the 2019 Linux Storage,Filesystem, and Memory-Management Summit, Roman Gushchin described problemshe has been facing with deleted control groups that take their time beforeactually going away. Some of these problems have been fixed, but the issuehas not been truly resolved.

Shakeel Butt started his 2019 Linux Storage, Filesystem, andMemory-Management Summit session by noting that memory makes up a big partof the total cost of equipping a data center. As a result, data-centeroperators try to make the best use of memory they can, generallyovercommitting it significantly. In this session, Butt described a schemein use at Google to try to improve memory utilization; while the need forthe described functionality was generally agreed upon, the developers inthe room were not entirely happy with the solution presented.

The performance of the fget() function in the kernel was the topicof a discussion led by Dave Watson at the 2019 Linux Storage, Filesystem,and Memory-Management Summit (LSFMM).fget() is used to take a reference to afile (i.e. bump a reference count), based on its file descriptor, and toreturn the struct file pointer for it; references are dropped withfput(). Some recent profiling at Watson'semployer, Facebook, found the function to be taking a sizable portion ofthe CPU time for some applications, so he wanted to talk about some of thethings he has tried to make that situation better.