I have been encountering a crash while attempting to emerge "rmagick" on a 512 MB Athlon TBird running the 2.6.12-r9 kernel. This first started happening in X windows and showed up as a hard lockup, so I rebooted the system without xdm and ran it from the console. I got an OOPS and a kernel panic labelled PRE-EMPT. I had the kernel configured with pre-empt *and* pre-empt the big kernel lock. This appears to be reproducible; something in the Ruby processing of rmagick triggers this. I have rebuilt the kernel without those configuration options and will attempt the emerge of rmagick again. I think it will work; it's worked on my other two Gentoo machines. I can try to track this down further, get all the stack trace data, etc., but I wanted to check with the kernel maintainers to see if this was a known upstream issue before I spend any more time on it. I have some free time over the weekend to go back to this, now that I know what it is and how to trigger it reproducibly.
Its hard to say with the little info you have provided. Oops messages say PREEMPT just to indicate that it is enabled, not to say that it is a PREEMPT-related problem (but it might be). We really need to see the oops message. Also you should try to reproduce this on gentoo-sources-2.6.13
I now know how to reproduce this ... I think. It turns out that what was happening is that the rmagick (1.3.2) ebuild was trying to write a huge file to disk and overflowed /var/tmp/portage (and hence /), causing the kernel to crash every time. So this is definitely a case of the kernel not being able to defend itself against a stupid user who tried to write more than a filesystem could handle. Once I cleaned up /var/tmp/portage/ rmagick emerged just fine. I don't know enough about the kernel to know whether the upstream folks know or care about this condition, but if there's some way to capture the stack trace, etc. for them, I'll go ahead and fill up /var/tmp/portage again, emerge rmagick again and ship the data to you all. Otherwise, you can close this as "user error".
You can either capture it over serial console, over netconsole, with a digital camera, or with pen-and-paper. Make sure you are running gentoo-sources-2.6.13 too, and give us more info (which filesystem is in use? emerge --info? etc)
Please reopen when you have time to provide us with more info (see comment #3)
