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Re: [RFC 1/2] tls: add macros for coroutine-safe TLS variables
From: |
Daniel P . Berrangé |
Subject: |
Re: [RFC 1/2] tls: add macros for coroutine-safe TLS variables |
Date: |
Mon, 25 Oct 2021 15:14:36 +0100 |
User-agent: |
Mutt/2.0.7 (2021-05-04) |
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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[RFC 2/2] util/async: replace __thread with QEMU TLS macros, Stefan Hajnoczi, 2021/10/25
Re: [RFC 0/2] tls: add macros for coroutine-safe TLS variables, Philippe Mathieu-Daudé, 2021/10/25