Prevent inconsistent CPU state after sequence of dlclose/dlopen

[Mathieu Desnoyers]

Hi,

I was discussing with Mark Rutland recently, and he pointed out that a
sequence of dlclose/dlopen mapping new code at the same addresses in
multithreaded environments is an issue on ARM, and possibly on Intel/AMD
with the newer TLB broadcast maintenance.

I maintain the membarrier(2) system call, which provides a
MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE command for this
purpose. It's been there since Linux 4.16. It can be configured
out (CONFIG_MEMBARRIER=n), but it's enabled by default.

Calling this after dlclose() in glibc would prevent this issue.

Is it handled in some other way, or should we open a bugzilla
entry to track this ?

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com