VLC hard-locks on Slackware

11 June 2017
Ever since I switched to Slackware it has involved quite a bit of manual effort, but there has only so far been one issue that is a real irritation: Playing of video files via VLC sometime causing the system to hard-lock, and the frequency of these crashes seemed to have at least an anecdotal link to the type of file being played. They were often enough to be a problem, and certainly irritating given that my previous Ubuntu 12.04 install that was rarely rebooted never once had such crashes. This affected both my laptop and desktop systems, so it was clearly a Slackware issue rather than a machine-specific one.

Driver issues

Doing some research I found a Ubuntu-related thread that pointed towards this being a buggy driver, which was believable as buggy user-land software should not normally crash the entire system.Using lspci it seems both systems have a Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09), which means both are using the same driver, although I am unsure whether the actual silicon is identical. I'm pretty sure the drivers in question is i915, which seems to cover a lot of Intel chipsets and functions.

While I have no doubt that Ubuntu has far more system testing than Slackware and quite likley has its own distribution-specific patches, I suspect the reason it was never a problem with my previous Ubuntu install was due to the Ubuntu 12.04 packages being too dated to enable enough of the troublesome features to cause crashes. Slackware doesn't update the kernel packages very often — at the moment it is on 4.4.38 and the 4.4.x stable series is currently upto 4.4.71 — but the Intel driver seems to be updated very frequently.

Sorting it out

From the Tools menu choose Preferences. If you have the Simple Preferences dialog, choose the Video tab and Accelerated video output (overlay). If you've got the Advanced Preferences dialog, select Video from the left-hand tree view and uncheck Overlay video output (it is about two-thirds of the way down the top set of checkboxes). For good measure probably should also restart VLC. I have not noticed any difference in performance as a result of disabling the hardware support, and more importantly it has not crashed since.

I don't know if choosing a specific video output module rather than Automatic would also fix the issue. To find out which module is being used, from the Tools menu choose Messages, select the Modules Tree tab, and find vout display in the tree control (it should be under libvlc → playlist → video output). On my desktop it defaults to xcb_glx (i.e. OpenGL GLX video output (XCB)).

Other affected software

In theory the same problem should affect other software, but I have yet to see any comparable trend of crashing with anything else that plays video streams. I have once had a crash while streaming video from the BBC in Chromium, but I cannot tell for sure whether this is the same issue as it may have been some other software running at the same time causing problems, and streaming from Youtube has never caused any problems. I don't recall mplayer ever crashing.