I was on the committee for Usenix WOOT, and this was one of my favorite submissions. But it has very little to do with concurrency or multicore CPUs. Watson's

I was on the committee for Usenix WOOT, and this was one of my favorite submissions. But it has very little to do with concurrency or multicore CPUs. Watson's paper points out that where there are indirections inside the kernel (for instance, filenames to vnodes), you have to be careful about TOCTTOU bugs. If you chase the same indirection twice, there is no guarantee you will arrive in the same place. This is a famous, hoary source of problems in userland. Watson's results were that things like Systrace (which firewall processes off from the rest of the system) have lots of TOCTTOU issues because they try to enforce policy on things like filenames. Because of the way they're architected, as a "layer" over/under the actual system call handlers, the security check and the actual system call do two seperate lookups. Race condition. This result doesn't depend on multicore; it happens on uniprocessor systems as well. TOCTTOU filesystem races in userland accounted for a good percentage of the 8lgm-era SunOS advisories.