LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20091105.mp3

For Thursday, November 5th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: CVE-2009-2584, Generic per-cpu counter arrays, MM locking, page types, performance events, and the scheduler.

CVE-2009-2584. A security issue was recently found in a procfs function contained within the sgi-gru driver. It involved unsafe use of strncpy_from_user. Various people posted fix suggestions for it, while Linus noted that most of the logic in the offending function (options_write) was “utter sh*t as far as I can tell”. He posted a couple of entirely untested patches (Linus style) for others to take a look at. Meanwhile, it was also noted that few people had the hardware, which helped to mitigate the issue.

Generic per-cpu counter arrays. Kamezawa Hiroyuki, noting that the patch had been “ony my queue for a month”, posted an RFC patch intended to add support for generic percpu counter arrays. His patch uses the recent dynamic percpu support to create arrays of per-cpu data on the fly, using some macros such as DEFINE_COUNTER_ARRAY, and functions such as counter_array_init, and counter_array_add to manage entries being added to an existing array.

MM locking. Christoph Lameter posted an RFC MM patch implementing a variety of “accessors for mm locking”. Essentially, the idea is to abstract and wrap up use of mmap_sem such that it could eventually be ripped out and replaced without having to touch a lot of MM code once again. Christoph notes that the patch is “currently incomplete” but it does at least build.

Page Types. Fengguang Wu posted a followup to his previous patch enabling one to specify new page type information on the command line of the “page-types” utility (used to decode various VM data) with an example of how one could educate page-types about new types of page flags on the command line.

Performance Events. Hitoshi Mitake posted version 5 of a 7 part patch series implementing the “perf bench” command, and incorporating Rusty Russell’s original “hackbench” scheduler benchmark code.

Scheduler. Lai Jiangshan noted that a previous patch from Mike Galbraith didn’t seem to be mitigating the problems with the scheduler running tasks on the wrong CPU. In his case, the built-in kernel thread named “events” for CPU 1 was in fact shown (by using Ftrace) to be running on CPU0. Mike noted that the problem was likely to be in the migration code not holding the runqueue lock and thus not being safe against pre-emption and subsequent chaos.

In today’s announcements: AlacrityVM version 0.2. Gregory Haskins announced the 0.2 release of his AlacrityVM project. This is a modified KVM that uses a replacement virtualized IO bus for improved performance of, for example, network packet transfer between host and guest. The latest version includes some nice features, such as zero-copy transmits in the VENET driver. For further informatin, visit:
http://developer.novell.com/wiki/index.php/AlacrityVM.

The latest kernel release is 2.6.32-rc6.

Stephen Rothwell posted a linux-next tree for November 5th. Since Wednesday, the PowerPC KVM fix was still around, while the pcmcia, drbd, and catalin trees lost their issues, and the sparc tree gained a build failure for which Stephen applied a patch. The total sub-tree count remained at 146 trees.

That’s a summary of today’s Linux Kernel Mailing List traffic, for further information visit www.kernel.org. I’m Jon Masters.