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Fix a memory order issue with weakly ordered systems

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this adds a dummy atomic release operation to update_qp, which
should make sure that the new value of reader_idx is visible in
get_hold_current_qp, directly after incrementing the users count.

Fixes: #26875

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26964)
This commit is contained in:
Bernd Edlinger 2025-03-03 23:46:12 +01:00 committed by Neil Horman
parent 5db7b99914
commit 4a1a7fe5ce
1 changed files with 7 additions and 0 deletions
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7
crypto/threads_pthread.c
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@ -407,6 +407,13 @@ static struct rcu_qp *update_qp(CRYPTO_RCU_LOCK *lock, uint32_t *curr_id)
ATOMIC_STORE_N(uint32_t, &lock->reader_idx, lock->current_alloc_idx,
__ATOMIC_RELAXED);
/*
* this should make sure that the new value of reader_idx is visible in
* get_hold_current_qp, directly after incrementing the users count
*/
ATOMIC_ADD_FETCH(&lock->qp_group[current_idx].users, (uint64_t)0,
__ATOMIC_RELEASE);
/* wake up any waiters */
pthread_cond_signal(&lock->alloc_signal);
pthread_mutex_unlock(&lock->alloc_lock);