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membarrier: introduce qemu/sys_membarrier.h

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This new header file provides heavy-weight "global" memory barriers that
enforce memory ordering on each running thread belonging to the current
process.  For now, use a dummy implementation that issues memory barriers
on both sides (matching what QEMU has been doing so far).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2018-02-16 10:04:18 +01:00
parent 77a8b8462b
commit c8d3877e48
3 changed files with 26 additions and 7 deletions
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9
util/rcu.c
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@ -93,10 +93,10 @@ static void wait_for_readers(void)
}
/* Here, order the stores to index->waiting before the loads of
* index->ctr. Pairs with smp_mb() in rcu_read_unlock(),
* index->ctr. Pairs with smp_mb_placeholder() in rcu_read_unlock(),
* ensuring that the loads of index->ctr are sequentially consistent.
*/
smp_mb();
smp_mb_global();
QLIST_FOREACH_SAFE(index, &registry, node, tmp) {
if (!rcu_gp_ongoing(&index->ctr)) {
@ -145,9 +145,9 @@ void synchronize_rcu(void)
qemu_mutex_lock(&rcu_sync_lock);
/* Write RCU-protected pointers before reading p_rcu_reader->ctr.
* Pairs with smp_mb() in rcu_read_lock().
* Pairs with smp_mb_placeholder() in rcu_read_lock().
*/
smp_mb();
smp_mb_global();
qemu_mutex_lock(&rcu_registry_lock);
if (!QLIST_EMPTY(&registry)) {
@ -376,6 +376,7 @@ static void rcu_init_child(void)
static void __attribute__((__constructor__)) rcu_init(void)
{
smp_mb_global_init();
#ifdef CONFIG_POSIX
pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
#endif