LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090624.mp3

For Wednesday, June 24th 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: NMI watchdog and NOHZ, upcoming kerneloops reports, the Simple Firmware Interface, Slow work module unload fixes, unevictable pages, and USB APIs.

The merge window is now closed, and it’s obvious from the drop-off in patches. Although as Stephen Rothwell noted, there are still a number of trees (14) in linux-next that need to be merged (or in American English, “punted”, to 2.6.32). As Stephen says, “please do not shoot the messenger.”

NMI watchdog and NOHZ. David Miller followed up (again) to his previously issue regarding nohz, this time arriving at the conclusion that little prevents the NMI firing if an interrupt storm arrives immediately after the call to tick_nohz_Stop_sched_tick(). Andi Kleen remarked that it would be safer to do tick disabling with interrupts off already, and that since the NMI watchdog is default off on most x86 systems, many people won’t have noticed.

Oops! The ever useful Arjan van de Ven posted a heads up regarding upcoming issues on kerneloops.org. Apparently, a lot of people have been bitten by an oops within get_page_from_freelist due to the changes to the VM intended to catch (and thoroughly blame) those calling kmalloc with __GFP_NOFAIL and order greater than zero. Unfortunately, this check turns out to be a little pedantic and there are many cases where legimate users need more than order 0 single page allocations returned (e.g. in the SLUB allocator). Linus Torvalds even followed up explaining how little difference there really is between order 0 and order 1, and how it shouldn’t be a big issue until you face allocations requesting order 3 or above. For now, it looks like order 1 and above is the magic number that the check will be updated to catch.

Simple Firmware Interface (SFI). Matthew Garrett followed up to his previous message concerning the SFI posting from the Intel camp. Previously, Matthew had objected to parts of the SFI concept – which is largely a cut-down ACPI – on the grounds that it tended to create a vendor mess of incompatible ACPI-like implementations with all manner of extension tables. Matthew feels that “SFI appears to be presented as a generic firmwae interface, but in reality it’s currently tightly wed to Moorestown [the Intel chipset] and I don’t see any way that that can be fixed without reinventing chunks of ACPI. I’m certainly not enthusiastic about seeing this present as a fait accompli in generic driver code”. One looks forward to the Linux Symposium “discussion”.

Slow work (if you can get it). Gregory Haskins posted a fix to the slow_work implementation, adding a module owner reference for module clients. Previously, the implementation did not have a means to ensure that slow-work threads had completely exited the text in question before it was yanked away by the module unload code.

Unevictable pages. Alok Kataria and Kamezawa Hiroyuki debated whether hugepages should be accounted as unevictable pages, and if so whether the name “unevictable” should be changed in procps output to “Pinned” or “Mlocked”. The problem is that, while hugepages are indeed unevictable, neither these nor the existing statistics fully account for every unevictable page present. Sometimes these aren’t known about even until vmscan tries to reclaim.

USB. There was some concern that lsusb was using an older API that stopped working unless CONFIG_EMBEDDED was set. This prompted several developers to question whether CONFIG_EMBEDDED should be required for “features” (it is intended to remove *unwanted* features), but Greg Kroah-Hartman explained that modern systems provide /dev/bus/usb and should be using that instead.

Miscellaneous updates include: A trivial update to the Intel TXT boot patches (Joseph Cihula, renaming a variable to make it global), IDE fixes (David Miller), Futex fixes (Thomas Gleixner, including the changes previously discussed to fault_in_user_writeable, fixing some incorrect assumptions in the previous patches regarding access_ok and whether a RW mapped region could go away under us), UWB (David Vrabel, trivial fixes), omapfb (Imre Deak, support for new LCDs and miscellaneous fixes), reducing the time taken for a single cpu online operation (Gautham R Shenoy, pseries), some networking updates (David Miller, mostly regular fixes), and a simplification of scripts/extract-ikconfig (Dick Streefland) removing the need for a special binary simply to extract a kernel config, which can be done in the bash script instead. David Airlie did try to post some drm-fixes, but it’s probably too late in the merge window at this point, as he noted.

Finally today, Mathieu Desnoyers asked about relicensing the marker LTTng, marker and tracepoints code under a dual license to include the lesser GPL license (LGPL v2.1). Although not objected to outright, some wondered why this was necessary, to which Mathieu responded that he wanted to allow userspace code that wanted to link to non-GPL code to still use the LTTng codebase.

The latest kernel release is 2.6.31-rc1, which was just released by Linus. Overall, Linus is extremely happy with how this merge window has gone. He adds, “On the whole? Tons of stuff. Let’s start testign and stabilizing.”

Stephen Rothwell posted a linux-next tree for June 24th. Since Tuesday, the fixes tree contains two commits fro fbdev and UML, the rr tree gained a conflict against Linus’ tree and the dwmw2-iommu tree lost its conflicts. The PowerPC tree still fails to build in an allyesconfig configuration.

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