According to Andrew Balsa, around the time of the discovery of the F00F bug on Intel Pentium, Serguei Shtyliov from Moscow found a flaw in a Cyrix processor while developing an IDE disk driver in assembly language.
Alexandr Konosevich, from Omsk, further researched the bug and coauthored an article with Uwe Post in the German technology magazine c't, calling it the "hidden CLI bug" (CLI is the instruction that disables interrupts in the x86 architecture).
Balsa, as a member on the Linux kernel mailing list, confirmed that the following C program (which uses inline x86-specific assembly language) could be compiled and run by an unprivileged user: Execution of this program renders the processor completely useless until it is rebooted, as it enters an infinite loop that cannot be interrupted.
This allows any user with access to a Cyrix system with this bug to perform a denial-of-service attack.
In order to ensure this atomicity, the designers at Cyrix made the xchg uninterruptible.