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Fix memory ordering for operations with quota->used and quota->waiting

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Change all the non-locked operations on 'quota->used' and
'quota->waiting' to "acq/rel" for inter-thread synchronization. Some
loads are left as "relaxed", because they are under a locked mutex
which also provides protection.
This commit is contained in:
Aram Sargsyan
2025-02-27 16:48:52 +00:00
committed by Arаm Sаrgsyаn
parent 80d7d11f37
commit df373d7d99
1 changed files with 8 additions and 6 deletions
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14
lib/isc/quota.c
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@@ -42,11 +42,10 @@ isc_quota_destroy(isc_quota_t *quota) {
REQUIRE(VALID_QUOTA(quota));
quota->magic = 0;
INSIST(atomic_load(&quota->used) == 0);
INSIST(atomic_load(&quota->waiting) == 0);
INSIST(atomic_load_acquire(&quota->used) == 0);
INSIST(atomic_load_acquire(&quota->waiting) == 0);
INSIST(ISC_LIST_EMPTY(quota->cbs));
atomic_store_relaxed(&quota->max, 0);
atomic_store_release(&quota->used, 0);
atomic_store_relaxed(&quota->soft, 0);
isc_mutex_destroy(&quota->cblock);
}
@@ -78,7 +77,7 @@ isc_quota_getsoft(isc_quota_t *quota) {
unsigned int
isc_quota_getused(isc_quota_t *quota) {
REQUIRE(VALID_QUOTA(quota));
return atomic_load_relaxed(&quota->used);
return atomic_load_acquire(&quota->used);
}
static isc_result_t
@@ -106,6 +105,7 @@ static void
enqueue(isc_quota_t *quota, isc_quota_cb_t *cb) {
REQUIRE(cb != NULL);
ISC_LIST_ENQUEUE(quota->cbs, cb, link);
/* No need for acquire; the lock protects from other writers. */
atomic_fetch_add_release(&quota->waiting, 1);
}
@@ -115,7 +115,8 @@ dequeue(isc_quota_t *quota) {
isc_quota_cb_t *cb = ISC_LIST_HEAD(quota->cbs);
INSIST(cb != NULL);
ISC_LIST_DEQUEUE(quota->cbs, cb, link);
atomic_fetch_sub_relaxed(&quota->waiting, 1);
/* No need for acquire; the lock protects from other writers. */
atomic_fetch_sub_release(&quota->waiting, 1);
return cb;
}
@@ -133,6 +134,7 @@ quota_release(isc_quota_t *quota) {
if (atomic_load_acquire(&quota->waiting) > 0) {
isc_quota_cb_t *cb = NULL;
LOCK(&quota->cblock);
/* No need for acquire; the lock protects from other writers. */
if (atomic_load_relaxed(&quota->waiting) > 0) {
cb = dequeue(quota);
}
@@ -143,7 +145,7 @@ quota_release(isc_quota_t *quota) {
}
}
used = atomic_fetch_sub_release(&quota->used, 1);
used = atomic_fetch_sub_acq_rel(&quota->used, 1);
INSIST(used > 0);
}