tmpfs can be induced to deadlock
Security researcher Hans Christian Woithe reported CVE-2021-43395 to both us and Oracle. He discovered conditions where any arbitrary user could induce tmpfs to panic with deadlock-detection. This bug tracks our fix for this problem.
Tested using Hans's PoC, which now does not induce a panic. Tested on OmniOS both bare-metal (by Andy Fiddaman) and VM (by Dan McD.). Tested on SmartOS bare-metal (by Dan McD.).