[openssl/openssl] f5a5e8: ensure writes are syncronized on windows in CRYPTO...

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: f5a5e89044174e1b9509841baa2b334b368bdadc
      https://github.com/openssl/openssl/commit/f5a5e89044174e1b9509841baa2b334b368bdadc
  Author: Neil Horman <[email protected]>
  Date:   2026-06-30 (Tue, 30 Jun 2026)

  Changed paths:
    M crypto/threads_win.c

  Log Message:
  -----------
  ensure writes are syncronized on windows in CRYPTO_THREAD_run_once

We've tried to fix this properly using InitOnceExecuteOnce, but it
results in an ABI breakage, so we're doing it this way.

on windows, CRYPTO_THREAD_run_once, on weakly memory ordered systems,
may complete the write of the run once variable lock before some of the
writes made by the init callback routine complete.  The result is that
on a heavily multithreaded application, other therads may see the data
that was meant to be in an initalized state, as in some erroneous
in-between state, leading to errors.

Fix it by inserting a full memory barrier after we return from the init
callback, and prior to setting the run once variable to ONCE_DONE.

Reviewed-by: Saša Nedvědický <[email protected]>
Reviewed-by: Nikola Pajkovsky <[email protected]>
Reviewed-by: Norbert Pocs <[email protected]>
MergeDate: Tue Jun 30 08:51:16 2026
(Merged from https://github.com/openssl/openssl/pull/31713)



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