One problem I’ve had recently on two systems with NVideo video cards is KMail crashing (SEGV) while reading mail. Sometimes it goes for months without having problems, and then it gets into a state where reading a few messages (or sometimes reading one particular message) causes a crash. The crash happens somewhere in the Mesa library stack.
In an attempt to investigate this I tried running KMail via ssh (as that precludes a lot of the GL stuff), but that crashed in a different way (I filed an upstream bug report ).
I have discovered a workaround for this issue, I set the environment variable LIBGL_ALWAYS_SOFTWARE=1 and then things work. At this stage I can’t be sure exactly where the problems are. As it’s certain KMail operations that trigger it I think that’s evidence of problems originating in KMail, but the end result when it happens often includes a kernel error log so there’s probably a problem in the Nouveau driver. I spent quite a lot of time investigating this, including recompiling most of the library stack with debugging mode and didn’t get much of a positive result. Hopefully putting it out there will help the next person who has such issues.
Here is a list of environment variables that can be set to debug LIBGL issues (strangely I couldn’t find documentation on this when Googling it). If you are stuck with a problem related to LIBGL you can try setting each of these to “1” in turn and see if it makes a difference. That can either be for the purpose of debugging a problem or creating a workaround that allows you to run the programs you need to run. I don’t know why GL is required to read email.