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Don't use rwlock upgrade/downgrade at all

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This commit is contained in:
Witold Kręcicki
2020-04-21 22:26:25 +02:00
parent 8a955ea403
commit c6f9262ce6
2 changed files with 31 additions and 70 deletions
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lib/dns/rbtdb.c
+29 -70
View File
@@ -167,8 +167,6 @@ typedef isc_rwlock_t nodelock_t;
#define NODE_DESTROYLOCK(l) isc_rwlock_destroy(l)
#define NODE_LOCK(l, t) RWLOCK((l), (t))
#define NODE_UNLOCK(l, t) RWUNLOCK((l), (t))
#define NODE_TRYUPGRADE(l) isc_rwlock_tryupgrade(l)
#define NODE_DOWNGRADE(l) isc_rwlock_downgrade(l)
/*%
* Whether to rate-limit updating the LRU to avoid possible thread contention.
@@ -2008,13 +2006,17 @@ reactivate_node(dns_rbtdb_t *rbtdb, dns_rbtnode_t *node,
static bool
decrement_reference(dns_rbtdb_t *rbtdb, dns_rbtnode_t *node,
rbtdb_serial_t least_serial, isc_rwlocktype_t nlock,
isc_rwlocktype_t *nlock_upgraded,
isc_rwlocktype_t tlock, bool pruning) {
isc_result_t result;
bool write_locked;
bool locked = tlock != isc_rwlocktype_none;
bool write_locked = tlock == isc_rwlocktype_write;
rbtdb_nodelock_t *nodelock;
int bucket = node->locknum;
bool no_reference = true;
INSIST(nlock == isc_rwlocktype_write || nlock_upgraded != NULL);
if (nlock_upgraded != NULL) {
*nlock_upgraded = nlock;
}
uint_fast32_t refs;
nodelock = &rbtdb->node_locks[bucket];
@@ -2036,15 +2038,12 @@ decrement_reference(dns_rbtdb_t *rbtdb, dns_rbtnode_t *node,
/* Upgrade the lock? */
if (nlock == isc_rwlocktype_read) {
*nlock_upgraded = isc_rwlocktype_write;
NODE_UNLOCK(&nodelock->lock, isc_rwlocktype_read);
NODE_LOCK(&nodelock->lock, isc_rwlocktype_write);
}
if (isc_refcount_decrement(&node->references) > 1) {
/* Restore the lock? */
if (nlock == isc_rwlocktype_read) {
NODE_DOWNGRADE(&nodelock->lock);
}
return (false);
}
@@ -2065,31 +2064,6 @@ decrement_reference(dns_rbtdb_t *rbtdb, dns_rbtnode_t *node,
}
}
/*
* Attempt to switch to a write lock on the tree. If this fails,
* we will add this node to a linked list of nodes in this locking
* bucket which we will free later.
*/
if (tlock != isc_rwlocktype_write) {
/*
* Locking hierarchy notwithstanding, we don't need to free
* the node lock before acquiring the tree write lock because
* we only do a trylock.
*/
if (tlock == isc_rwlocktype_read) {
result = isc_rwlock_tryupgrade(&rbtdb->tree_lock);
} else {
result = isc_rwlock_trylock(&rbtdb->tree_lock,
isc_rwlocktype_write);
}
RUNTIME_CHECK(result == ISC_R_SUCCESS ||
result == ISC_R_LOCKBUSY);
write_locked = (result == ISC_R_SUCCESS);
} else {
write_locked = true;
}
refs = isc_refcount_decrement(&nodelock->references);
INSIST(refs > 0);
@@ -2134,24 +2108,6 @@ decrement_reference(dns_rbtdb_t *rbtdb, dns_rbtnode_t *node,
restore_locks:
/* Restore the lock? */
if (nlock == isc_rwlocktype_read) {
NODE_DOWNGRADE(&nodelock->lock);
}
/*
* Relock a read lock, or unlock the write lock if no lock was held.
*/
if (tlock == isc_rwlocktype_none) {
if (write_locked) {
RWUNLOCK(&rbtdb->tree_lock, isc_rwlocktype_write);
}
}
if (tlock == isc_rwlocktype_read) {
if (write_locked) {
isc_rwlock_downgrade(&rbtdb->tree_lock);
}
}
return (no_reference);
}
@@ -2179,7 +2135,7 @@ prune_tree(isc_task_t *task, isc_event_t *event) {
NODE_LOCK(&rbtdb->node_locks[locknum].lock, isc_rwlocktype_write);
do {
parent = node->parent;
decrement_reference(rbtdb, node, 0, isc_rwlocktype_write,
decrement_reference(rbtdb, node, 0, isc_rwlocktype_write, NULL,
isc_rwlocktype_write, true);
if (parent != NULL && parent->down == NULL) {
@@ -2644,7 +2600,7 @@ closeversion(dns_db_t *db, dns_dbversion_t **versionp, bool commit) {
}
}
decrement_reference(rbtdb, header->node, least_serial,
isc_rwlocktype_write, isc_rwlocktype_none,
isc_rwlocktype_write, NULL, isc_rwlocktype_none,
false);
NODE_UNLOCK(lock, isc_rwlocktype_write);
}
@@ -2694,7 +2650,7 @@ closeversion(dns_db_t *db, dns_dbversion_t **versionp, bool commit) {
rollback_node(rbtnode, serial);
}
decrement_reference(rbtdb, rbtnode, least_serial,
isc_rwlocktype_write, tlock, false);
isc_rwlocktype_write, NULL, tlock, false);
NODE_UNLOCK(lock, isc_rwlocktype_write);
@@ -4404,9 +4360,10 @@ tree_exit:
lock = &(search.rbtdb->node_locks[node->locknum].lock);
NODE_LOCK(lock, isc_rwlocktype_read);
isc_rwlocktype_t nlock;
decrement_reference(search.rbtdb, node, 0, isc_rwlocktype_read,
isc_rwlocktype_none, false);
NODE_UNLOCK(lock, isc_rwlocktype_read);
&nlock, isc_rwlocktype_none, false);
NODE_UNLOCK(lock, nlock);
}
if (close_version) {
@@ -4443,6 +4400,7 @@ static bool
check_stale_header(dns_rbtnode_t *node, rdatasetheader_t *header,
isc_rwlocktype_t *locktype, nodelock_t *lock,
rbtdb_search_t *search, rdatasetheader_t **header_prev) {
UNUSED(lock);
if (!ACTIVE(header, search->now)) {
dns_ttl_t stale = header->rdh_ttl +
search->rbtdb->serve_stale_ttl;
@@ -4464,8 +4422,7 @@ check_stale_header(dns_rbtnode_t *node, rdatasetheader_t *header,
* cleaned up later.
*/
if ((header->rdh_ttl < search->now - RBTDB_VIRTUAL) &&
(*locktype == isc_rwlocktype_write ||
NODE_TRYUPGRADE(lock) == ISC_R_SUCCESS))
(*locktype == isc_rwlocktype_write))
{
/*
* We update the node's status only when we can
@@ -5153,9 +5110,10 @@ tree_exit:
lock = &(search.rbtdb->node_locks[node->locknum].lock);
NODE_LOCK(lock, isc_rwlocktype_read);
isc_rwlocktype_t nlock;
decrement_reference(search.rbtdb, node, 0, isc_rwlocktype_read,
isc_rwlocktype_none, false);
NODE_UNLOCK(lock, isc_rwlocktype_read);
&nlock, isc_rwlocktype_none, false);
NODE_UNLOCK(lock, nlock);
}
dns_rbtnodechain_reset(&search.chain);
@@ -5348,8 +5306,8 @@ detachnode(dns_db_t *db, dns_dbnode_t **targetp) {
nodelock = &rbtdb->node_locks[node->locknum];
NODE_LOCK(&nodelock->lock, isc_rwlocktype_read);
if (decrement_reference(rbtdb, node, 0, isc_rwlocktype_read,
isc_rwlocktype_t nlock;
if (decrement_reference(rbtdb, node, 0, isc_rwlocktype_read, &nlock,
isc_rwlocktype_none, false))
{
if (isc_refcount_current(&nodelock->references) == 0 &&
@@ -5358,7 +5316,7 @@ detachnode(dns_db_t *db, dns_dbnode_t **targetp) {
}
}
NODE_UNLOCK(&nodelock->lock, isc_rwlocktype_read);
NODE_UNLOCK(&nodelock->lock, nlock);
*targetp = NULL;
@@ -5710,8 +5668,7 @@ cache_findrdataset(dns_db_t *db, dns_dbnode_t *node, dns_dbversion_t *version,
header_next = header->next;
if (!ACTIVE(header, now)) {
if ((header->rdh_ttl < now - RBTDB_VIRTUAL) &&
(locktype == isc_rwlocktype_write ||
NODE_TRYUPGRADE(lock) == ISC_R_SUCCESS))
(locktype == isc_rwlocktype_write))
{
/*
* We update the node's status only when we
@@ -9171,9 +9128,10 @@ dereference_iter_node(rbtdb_dbiterator_t *rbtdbiter) {
lock = &rbtdb->node_locks[node->locknum].lock;
NODE_LOCK(lock, isc_rwlocktype_read);
isc_rwlocktype_t nlock;
decrement_reference(rbtdb, node, 0, isc_rwlocktype_read,
rbtdbiter->tree_locked, false);
NODE_UNLOCK(lock, isc_rwlocktype_read);
&nlock, rbtdbiter->tree_locked, false);
NODE_UNLOCK(lock, nlock);
rbtdbiter->node = NULL;
}
@@ -9211,9 +9169,10 @@ flush_deletions(rbtdb_dbiterator_t *rbtdbiter) {
lock = &rbtdb->node_locks[node->locknum].lock;
NODE_LOCK(lock, isc_rwlocktype_read);
isc_rwlocktype_t nlock;
decrement_reference(rbtdb, node, 0, isc_rwlocktype_read,
rbtdbiter->tree_locked, false);
NODE_UNLOCK(lock, isc_rwlocktype_read);
&nlock, rbtdbiter->tree_locked, false);
NODE_UNLOCK(lock, nlock);
}
rbtdbiter->delcnt = 0;
@@ -10506,7 +10465,7 @@ expire_header(dns_rbtdb_t *rbtdb, rdatasetheader_t *header, bool tree_locked,
*/
new_reference(rbtdb, header->node);
decrement_reference(rbtdb, header->node, 0,
isc_rwlocktype_write,
isc_rwlocktype_write, NULL,
tree_locked ? isc_rwlocktype_write
: isc_rwlocktype_none,
false);
lib/isc/rwlock.c
+2
View File
@@ -513,6 +513,7 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
isc_result_t
isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
INSIST(0);
REQUIRE(VALID_RWLOCK(rwl));
int_fast32_t reader_incr = READER_INCR;
@@ -542,6 +543,7 @@ isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
void
isc_rwlock_downgrade(isc_rwlock_t *rwl) {
INSIST(0);
int32_t prev_readers;
REQUIRE(VALID_RWLOCK(rwl));