CVE 2006-1066
Linux kernel 2.6.16-rc2 and earlier, when running on x86_64 systems with preemption enabled, allows local users to cause a denial of service (oops) via multiple ptrace tasks that perform single steps, which can cause corruption of the DEBUG_STACK stack during the do_debug function call.
See the 
CVE page on Mitre.org
for more details.
