* IBM's contributions to this file may be relicensed under LGPLv2 or later.
*/
-#include "qemu-common.h"
-#include <stdio.h>
-#include <assert.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <errno.h>
+#include "qemu/osdep.h"
#include "qemu/rcu.h"
#include "qemu/atomic.h"
#include "qemu/thread.h"
+#include "qemu/main-loop.h"
+#include "qemu/lockable.h"
+#if defined(CONFIG_MALLOC_TRIM)
+#include <malloc.h>
+#endif
/*
* Global grace period counter. Bit 0 is always one in rcu_gp_ctr.
unsigned long rcu_gp_ctr = RCU_GP_LOCKED;
QemuEvent rcu_gp_event;
-static QemuMutex rcu_gp_lock;
+static int in_drain_call_rcu;
+static QemuMutex rcu_registry_lock;
+static QemuMutex rcu_sync_lock;
/*
* Check whether a quiescent state was crossed between the beginning of
{
unsigned long v;
- v = atomic_read(ctr);
+ v = qatomic_read(ctr);
return v && (v != rcu_gp_ctr);
}
*/
__thread struct rcu_reader_data rcu_reader;
-/* Protected by rcu_gp_lock. */
+/* Protected by rcu_registry_lock. */
typedef QLIST_HEAD(, rcu_reader_data) ThreadList;
static ThreadList registry = QLIST_HEAD_INITIALIZER(registry);
*/
qemu_event_reset(&rcu_gp_event);
- /* Instead of using atomic_mb_set for index->waiting, and
- * atomic_mb_read for index->ctr, memory barriers are placed
+ /* Instead of using qatomic_mb_set for index->waiting, and
+ * qatomic_mb_read for index->ctr, memory barriers are placed
* manually since writes to different threads are independent.
- * atomic_mb_set has a smp_wmb before...
+ * qemu_event_reset has acquire semantics, so no memory barrier
+ * is needed here.
*/
- smp_wmb();
QLIST_FOREACH(index, ®istry, node) {
- atomic_set(&index->waiting, true);
+ qatomic_set(&index->waiting, true);
}
- /* ... and a smp_mb after. */
- smp_mb();
+ /* Here, order the stores to index->waiting before the loads of
+ * index->ctr. Pairs with smp_mb_placeholder() in rcu_read_unlock(),
+ * ensuring that the loads of index->ctr are sequentially consistent.
+ */
+ smp_mb_global();
QLIST_FOREACH_SAFE(index, ®istry, node, tmp) {
if (!rcu_gp_ongoing(&index->ctr)) {
/* No need for mb_set here, worst of all we
* get some extra futex wakeups.
*/
- atomic_set(&index->waiting, false);
+ qatomic_set(&index->waiting, false);
+ } else if (qatomic_read(&in_drain_call_rcu)) {
+ notifier_list_notify(&index->force_rcu, NULL);
}
}
- /* atomic_mb_read has smp_rmb after. */
- smp_rmb();
-
if (QLIST_EMPTY(®istry)) {
break;
}
- /* Wait for one thread to report a quiescent state and
- * try again.
+ /* Wait for one thread to report a quiescent state and try again.
+ * Release rcu_registry_lock, so rcu_(un)register_thread() doesn't
+ * wait too much time.
+ *
+ * rcu_register_thread() may add nodes to ®istry; it will not
+ * wake up synchronize_rcu, but that is okay because at least another
+ * thread must exit its RCU read-side critical section before
+ * synchronize_rcu is done. The next iteration of the loop will
+ * move the new thread's rcu_reader from ®istry to &qsreaders,
+ * because rcu_gp_ongoing() will return false.
+ *
+ * rcu_unregister_thread() may remove nodes from &qsreaders instead
+ * of ®istry if it runs during qemu_event_wait. That's okay;
+ * the node then will not be added back to ®istry by QLIST_SWAP
+ * below. The invariant is that the node is part of one list when
+ * rcu_registry_lock is released.
*/
+ qemu_mutex_unlock(&rcu_registry_lock);
qemu_event_wait(&rcu_gp_event);
+ qemu_mutex_lock(&rcu_registry_lock);
}
/* put back the reader list in the registry */
void synchronize_rcu(void)
{
- qemu_mutex_lock(&rcu_gp_lock);
+ QEMU_LOCK_GUARD(&rcu_sync_lock);
+ /* Write RCU-protected pointers before reading p_rcu_reader->ctr.
+ * Pairs with smp_mb_placeholder() in rcu_read_lock().
+ */
+ smp_mb_global();
+
+ QEMU_LOCK_GUARD(&rcu_registry_lock);
if (!QLIST_EMPTY(®istry)) {
- /* In either case, the atomic_mb_set below blocks stores that free
+ /* In either case, the qatomic_mb_set below blocks stores that free
* old RCU-protected pointers.
*/
if (sizeof(rcu_gp_ctr) < 8) {
*
* Switch parity: 0 -> 1, 1 -> 0.
*/
- atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+ qatomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
wait_for_readers();
- atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
+ qatomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
} else {
/* Increment current grace period. */
- atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
+ qatomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
}
wait_for_readers();
}
-
- qemu_mutex_unlock(&rcu_gp_lock);
}
struct rcu_head **old_tail;
node->next = NULL;
- old_tail = atomic_xchg(&tail, &node->next);
- atomic_mb_set(old_tail, node);
+ old_tail = qatomic_xchg(&tail, &node->next);
+ qatomic_mb_set(old_tail, node);
}
static struct rcu_head *try_dequeue(void)
* The tail, because it is the first step in the enqueuing.
* It is only the next pointers that might be inconsistent.
*/
- if (head == &dummy && atomic_mb_read(&tail) == &dummy.next) {
+ if (head == &dummy && qatomic_mb_read(&tail) == &dummy.next) {
abort();
}
* wrong and we need to wait until its enqueuer finishes the update.
*/
node = head;
- next = atomic_mb_read(&head->next);
+ next = qatomic_mb_read(&head->next);
if (!next) {
return NULL;
}
{
struct rcu_head *node;
+ rcu_register_thread();
+
for (;;) {
int tries = 0;
- int n = atomic_read(&rcu_call_count);
+ int n = qatomic_read(&rcu_call_count);
/* Heuristically wait for a decent number of callbacks to pile up.
* Fetch rcu_call_count now, we only must process elements that were
* added before synchronize_rcu() starts.
*/
- while (n < RCU_CALL_MIN_SIZE && ++tries <= 5) {
- g_usleep(100000);
- qemu_event_reset(&rcu_call_ready_event);
- n = atomic_read(&rcu_call_count);
- if (n < RCU_CALL_MIN_SIZE) {
- qemu_event_wait(&rcu_call_ready_event);
- n = atomic_read(&rcu_call_count);
+ while (n == 0 || (n < RCU_CALL_MIN_SIZE && ++tries <= 5)) {
+ g_usleep(10000);
+ if (n == 0) {
+ qemu_event_reset(&rcu_call_ready_event);
+ n = qatomic_read(&rcu_call_count);
+ if (n == 0) {
+#if defined(CONFIG_MALLOC_TRIM)
+ malloc_trim(4 * 1024 * 1024);
+#endif
+ qemu_event_wait(&rcu_call_ready_event);
+ }
}
+ n = qatomic_read(&rcu_call_count);
}
- atomic_sub(&rcu_call_count, n);
+ qatomic_sub(&rcu_call_count, n);
synchronize_rcu();
+ qemu_mutex_lock_iothread();
while (n > 0) {
node = try_dequeue();
while (!node) {
+ qemu_mutex_unlock_iothread();
qemu_event_reset(&rcu_call_ready_event);
node = try_dequeue();
if (!node) {
qemu_event_wait(&rcu_call_ready_event);
node = try_dequeue();
}
+ qemu_mutex_lock_iothread();
}
n--;
node->func(node);
}
+ qemu_mutex_unlock_iothread();
}
abort();
}
{
node->func = func;
enqueue(node);
- atomic_inc(&rcu_call_count);
+ qatomic_inc(&rcu_call_count);
qemu_event_set(&rcu_call_ready_event);
}
+
+struct rcu_drain {
+ struct rcu_head rcu;
+ QemuEvent drain_complete_event;
+};
+
+static void drain_rcu_callback(struct rcu_head *node)
+{
+ struct rcu_drain *event = (struct rcu_drain *)node;
+ qemu_event_set(&event->drain_complete_event);
+}
+
+/*
+ * This function ensures that all pending RCU callbacks
+ * on the current thread are done executing
+
+ * drops big qemu lock during the wait to allow RCU thread
+ * to process the callbacks
+ *
+ */
+
+void drain_call_rcu(void)
+{
+ struct rcu_drain rcu_drain;
+ bool locked = qemu_mutex_iothread_locked();
+
+ memset(&rcu_drain, 0, sizeof(struct rcu_drain));
+ qemu_event_init(&rcu_drain.drain_complete_event, false);
+
+ if (locked) {
+ qemu_mutex_unlock_iothread();
+ }
+
+
+ /*
+ * RCU callbacks are invoked in the same order as in which they
+ * are registered, thus we can be sure that when 'drain_rcu_callback'
+ * is called, all RCU callbacks that were registered on this thread
+ * prior to calling this function are completed.
+ *
+ * Note that since we have only one global queue of the RCU callbacks,
+ * we also end up waiting for most of RCU callbacks that were registered
+ * on the other threads, but this is a side effect that shoudn't be
+ * assumed.
+ */
+
+ qatomic_inc(&in_drain_call_rcu);
+ call_rcu1(&rcu_drain.rcu, drain_rcu_callback);
+ qemu_event_wait(&rcu_drain.drain_complete_event);
+ qatomic_dec(&in_drain_call_rcu);
+
+ if (locked) {
+ qemu_mutex_lock_iothread();
+ }
+
+}
+
void rcu_register_thread(void)
{
assert(rcu_reader.ctr == 0);
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
QLIST_INSERT_HEAD(®istry, &rcu_reader, node);
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
}
void rcu_unregister_thread(void)
{
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
QLIST_REMOVE(&rcu_reader, node);
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
}
-static void __attribute__((__constructor__)) rcu_init(void)
+void rcu_add_force_rcu_notifier(Notifier *n)
+{
+ qemu_mutex_lock(&rcu_registry_lock);
+ notifier_list_add(&rcu_reader.force_rcu, n);
+ qemu_mutex_unlock(&rcu_registry_lock);
+}
+
+void rcu_remove_force_rcu_notifier(Notifier *n)
+{
+ qemu_mutex_lock(&rcu_registry_lock);
+ notifier_remove(n);
+ qemu_mutex_unlock(&rcu_registry_lock);
+}
+
+static void rcu_init_complete(void)
{
QemuThread thread;
- qemu_mutex_init(&rcu_gp_lock);
+ qemu_mutex_init(&rcu_registry_lock);
+ qemu_mutex_init(&rcu_sync_lock);
qemu_event_init(&rcu_gp_event, true);
qemu_event_init(&rcu_call_ready_event, false);
+
+ /* The caller is assumed to have iothread lock, so the call_rcu thread
+ * must have been quiescent even after forking, just recreate it.
+ */
qemu_thread_create(&thread, "call_rcu", call_rcu_thread,
NULL, QEMU_THREAD_DETACHED);
rcu_register_thread();
}
+
+static int atfork_depth = 1;
+
+void rcu_enable_atfork(void)
+{
+ atfork_depth++;
+}
+
+void rcu_disable_atfork(void)
+{
+ atfork_depth--;
+}
+
+#ifdef CONFIG_POSIX
+static void rcu_init_lock(void)
+{
+ if (atfork_depth < 1) {
+ return;
+ }
+
+ qemu_mutex_lock(&rcu_sync_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
+}
+
+static void rcu_init_unlock(void)
+{
+ if (atfork_depth < 1) {
+ return;
+ }
+
+ qemu_mutex_unlock(&rcu_registry_lock);
+ qemu_mutex_unlock(&rcu_sync_lock);
+}
+
+static void rcu_init_child(void)
+{
+ if (atfork_depth < 1) {
+ return;
+ }
+
+ memset(®istry, 0, sizeof(registry));
+ rcu_init_complete();
+}
+#endif
+
+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
+ rcu_init_complete();
+}
projects / mirror_qemu.git / blobdiff