Re: [RFC 1/2] tls: add macros for coroutine-safe TLS variables

[Daniel P . Berrangé]

On Mon, Oct 25, 2021 at 03:07:15PM +0100, Stefan Hajnoczi wrote:
> Compiler optimizations can cache TLS values across coroutine yield
> points, resulting in stale values from the previous thread when a
> coroutine is re-entered by a new thread.
> 
> Serge Guelton developed an __attribute__((noinline)) wrapper and tested
> it with clang and gcc. I formatted his idea according to QEMU's coding
> style and wrote documentation.
> 
> These macros must be used instead of __thread from now on to prevent
> coroutine TLS bugs.

Does this apply to all  __thread usage in the QEMU process that can
be used from coroutine context, or just certain __thread usage ?

Mostly I'm wondering if this is going to have implications on external
libraries we use. eg if block layer is using librbd.so APIs, is librbd.sp
safe to use __thread directly in any way it desires ?


Regards,
Daniel
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