[openssl/openssl] 984595: ensure writes are syncronized on windows in CRYPTO...

  Branch: refs/heads/openssl-3.4
  Home:   https://github.com/openssl/openssl
  Commit: 9845957737970297a8c5b2eecea41ee3370bbbb9
      https://github.com/openssl/openssl/commit/9845957737970297a8c5b2eecea41ee3370bbbb9
  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 08:52:11 2026
(Merged from https://github.com/openssl/openssl/pull/31713)



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