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rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu() 

If rcu_(un)register_thread() is called together with synchronize_rcu(),
it will wait for the synchronize_rcu() to finish. But when synchronize_rcu()
waits for some events, we can modify the list registry.
We also use the lock rcu_gp_lock to assume that synchronize_rcu() isn't
executed in more than one thread at the same time. Add a new mutex lock
rcu_sync_lock to assume it and rename rcu_gp_lock to rcu_registry_lock.
Release rcu_registry_lock when synchronize_rcu() waits for some events.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Message-Id: <55B59652.4090503@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
master
Wen Congyang 2015-07-27 10:24:18 +08:00 committed by Paolo Bonzini
parent 414b15c909
commit c097a60b10
1 changed files with 35 additions and 13 deletions
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48
util/rcu.c
View File

@ -47,7 +47,8 @@
unsigned long rcu_gp_ctr = RCU_GP_LOCKED;
QemuEvent rcu_gp_event;
static QemuMutex rcu_gp_lock;
static QemuMutex rcu_registry_lock;
static QemuMutex rcu_sync_lock;
/*
* Check whether a quiescent state was crossed between the beginning of
@ -66,7 +67,7 @@ static inline int rcu_gp_ongoing(unsigned long *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);
@ -114,10 +115,26 @@ static void wait_for_readers(void)
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 &registry; 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 &registry to &qsreaders,
* because rcu_gp_ongoing() will return false.
*
* rcu_unregister_thread() may remove nodes from &qsreaders instead
* of &registry if it runs during qemu_event_wait. That's okay;
* the node then will not be added back to &registry 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 */
@ -126,7 +143,8 @@ static void wait_for_readers(void)
void synchronize_rcu(void)
{
qemu_mutex_lock(&rcu_gp_lock);
qemu_mutex_lock(&rcu_sync_lock);
qemu_mutex_lock(&rcu_registry_lock);
if (!QLIST_EMPTY(&registry)) {
/* In either case, the atomic_mb_set below blocks stores that free
@ -149,7 +167,8 @@ void synchronize_rcu(void)
wait_for_readers();
}
qemu_mutex_unlock(&rcu_gp_lock);
qemu_mutex_unlock(&rcu_registry_lock);
qemu_mutex_unlock(&rcu_sync_lock);
}
@ -273,23 +292,24 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node))
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(&registry, &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 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);
@ -306,12 +326,14 @@ static void rcu_init_complete(void)
#ifdef CONFIG_POSIX
static void rcu_init_lock(void)
{
qemu_mutex_lock(&rcu_gp_lock);
qemu_mutex_lock(&rcu_sync_lock);
qemu_mutex_lock(&rcu_registry_lock);
}
static void rcu_init_unlock(void)
{
qemu_mutex_unlock(&rcu_gp_lock);
qemu_mutex_unlock(&rcu_registry_lock);
qemu_mutex_unlock(&rcu_sync_lock);
}
#endif