LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20100124.mp3

For the weekend of January 24th, 2010, I’m Jon Masters with a summary of the week’s LKML traffic.

Linux 2.6.33-rc5. Linus Torvalds announced the release of the 2.6.33-rc5 kernel, noting that he didn’t “think there is anything earth-shaking here”. Mostly, the only new stuff was in the i915 and (new) DVB “Mantis” driver. Rafael J. Wysocki followed up with his usual list of regressions since the release of 2.6.32, for which there were no know fixes yet in Linus’ tree. The number has fallen a little, but there were still 23 unresolved.

devtmpfs. The devtmpfs filesystem is a shared memory filesystem used to mount /dev nodes that are needed even before udev starts on modern Linux systems (or for those systems that do not use udev, to provide a minimum environment). The suggestion had been made to remove the EXPERIMENTAL flag on its configuration option and enable it by default. The latter received complaints as a change in behavior that would be visible to users, even if many of them would need to have devtmpfs enabled for the most recent Linux distributions.

Interruptions. Steven Rostedt, and Peter Zijlstra did some analysis of the kernel source tree, looking for inappropriate setting of TASK_*INTERRUPTIBLE (which should never be done explicitly, and in general one should always use the set_current_state macro). They found a fairly large number of incorrect code paths and posted a list of “examples of likely bugs”. David Daney replied, asking what kind of barrier should be implied in using set_current_state, as pertains to the visibility of this assignment by other CPUs.

IO error semantics. Nick Piggin started a thread entitled “IO error semantics”, in which he raised the ugly issue of kernel IO error handling behavior once again, as he said he had done during Andi Kleen’s posting of HWPOISON patches. Nick sought to clearly define specific anticipated behaviors in response to “read IOs”, “write IOs”, and so forth – how many retries? etc. He also made the point that write IO errors should not invalidate the data before an IO error is returned to “somebody” (fsync or synchronous write syscall).

NOIO. Rafael J. Wysocki posted an initial PM patch implementing forced GFP_NOIO during suspend operations (preventing the kernel from attempting to allocate memory by going to e.g. disk to offload some existing unused pages), this was largely in reaction to specific issues with the Nvidia closed source binary driver, but was something that had apparently been on the cards for some time. The problem with the patch was that it changed the VM according to the state of the system, rather than relying upon drivers to do the right thing in using explicit GFP_NOIO allocations during suspend and resume routines.

In the week’s miscellaneous items: Tejun Heo posted version 3 of his concurrency managed workqueue patches, Peter Anvin proposed the rapid removal of CONFIG_X86_CPU_DEBUG (since all such information is already exposed elsewhere), the addition of “nopat” boot option documentation to Documentation/kernel-paramters by Jiri Kosina, ongoing discussion of generalization of certain PCI functions in the wake of and intention to merge various Xilinx PCI support bits, a cache coherency problem with mmaped writes on ARM systems posted by Anfei Zhou, a patch correcting priority inheritance deboosting in the RT kernel patchset to be POSIX compliant, Dimitry Golubovsky inquired as to the current state of UML (User Mode Linux, not the silly and pointless modelling technique) development, some Restricted Access Register (Intel MID platform) patches from Mark Allyn, and a large number of floppy (yes, floppy) cleanups from Joe Perches.

In the week’s announcements: Linux 2.6.31.12 and 2.6.32.5 (proceeded by the 2.6.32.4 kernel earlier in the week) were released by Greg Kroah-Hartman. Greg stated that he no longer intended to update the .31 stable kernel short of “something really odd happening”. Greg repeated his previous assertions that the .27 kernel would live on as a “long term” stable release (but probably only for 6 more months of viability), and that the .32 kernel would also be a “long term release” because a number of distributions were apparently basing their distributions around it. His efforts depend upon engineers working on those distributions to help.

Len Brown announced that the Linux Power Management Mini-Summit would be held in Boston on Monday, August 9th 2010, the day before the LinuxCon 2010. For further information, refer to http://events.linuxfoundation.org/.

Mathieu Desnoyers (whose excellent PhD thesis was published recently and covered by LWN) announced an updated LTTng 0.187 for the 2.6.32.4 kernel.

Junio C Hamano announced Git 1.6.6.1 is now available from the kernel.org site at http://www.kernel.org/pub/software/scm/git/. The latest version contains fixes for issues such as “git blame” not working when a commit lacked an author name, “git count-objects” not handling packfiles larger than 4G on platforms with a 32-bit off_t, “git rebase -i” not aborting cleaning if it failed to start the user’s EDITOR, some issues with
the GIT_WORK_TREE environment variable, and more besides.

Thomas Gleixner announced the release of 2.6.31.12-rt20 RT patchset. This was a forward port to 2.6.31.12, which included a number of RCU assumption fixes, the aforementioned PI POSIX compliance fix, and so forth. Thomas noted the delay in releasing a new version of the patch, but noted that various locking infrastructure changes had gone upstream (advancing the cause of mainlining various bits of RT). There will be no 2.6.32-rt, but will skip directly over to 2.6.33. He also let us know about a new “housemate” of his: http://tglx.de/~tglx/housemate.png.

Sorry for the delay in getting this episode released.