mirror of https://github.com/proxmox/mirror_qemu
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
parent
414b15c909
commit
c097a60b10
48
util/rcu.c
48
util/rcu.c
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@ -47,7 +47,8 @@
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unsigned long rcu_gp_ctr = RCU_GP_LOCKED;
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unsigned long rcu_gp_ctr = RCU_GP_LOCKED;
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QemuEvent rcu_gp_event;
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QemuEvent rcu_gp_event;
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static QemuMutex rcu_gp_lock;
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static QemuMutex rcu_registry_lock;
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static QemuMutex rcu_sync_lock;
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/*
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/*
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* Check whether a quiescent state was crossed between the beginning of
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* Check whether a quiescent state was crossed between the beginning of
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@ -66,7 +67,7 @@ static inline int rcu_gp_ongoing(unsigned long *ctr)
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*/
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*/
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__thread struct rcu_reader_data rcu_reader;
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__thread struct rcu_reader_data rcu_reader;
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/* Protected by rcu_gp_lock. */
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/* Protected by rcu_registry_lock. */
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typedef QLIST_HEAD(, rcu_reader_data) ThreadList;
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typedef QLIST_HEAD(, rcu_reader_data) ThreadList;
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static ThreadList registry = QLIST_HEAD_INITIALIZER(registry);
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static ThreadList registry = QLIST_HEAD_INITIALIZER(registry);
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@ -114,10 +115,26 @@ static void wait_for_readers(void)
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break;
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break;
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}
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}
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/* Wait for one thread to report a quiescent state and
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/* Wait for one thread to report a quiescent state and try again.
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* try again.
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* Release rcu_registry_lock, so rcu_(un)register_thread() doesn't
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* wait too much time.
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*
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* rcu_register_thread() may add nodes to ®istry; it will not
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* wake up synchronize_rcu, but that is okay because at least another
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* thread must exit its RCU read-side critical section before
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* synchronize_rcu is done. The next iteration of the loop will
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* move the new thread's rcu_reader from ®istry to &qsreaders,
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* because rcu_gp_ongoing() will return false.
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*
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* rcu_unregister_thread() may remove nodes from &qsreaders instead
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* of ®istry if it runs during qemu_event_wait. That's okay;
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* the node then will not be added back to ®istry by QLIST_SWAP
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* below. The invariant is that the node is part of one list when
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* rcu_registry_lock is released.
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*/
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*/
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qemu_mutex_unlock(&rcu_registry_lock);
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qemu_event_wait(&rcu_gp_event);
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qemu_event_wait(&rcu_gp_event);
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qemu_mutex_lock(&rcu_registry_lock);
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}
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}
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/* put back the reader list in the registry */
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/* put back the reader list in the registry */
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@ -126,7 +143,8 @@ static void wait_for_readers(void)
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void synchronize_rcu(void)
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void synchronize_rcu(void)
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{
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{
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qemu_mutex_lock(&rcu_gp_lock);
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qemu_mutex_lock(&rcu_sync_lock);
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qemu_mutex_lock(&rcu_registry_lock);
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if (!QLIST_EMPTY(®istry)) {
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if (!QLIST_EMPTY(®istry)) {
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/* In either case, the atomic_mb_set below blocks stores that free
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/* In either case, the atomic_mb_set below blocks stores that free
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@ -149,7 +167,8 @@ void synchronize_rcu(void)
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wait_for_readers();
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wait_for_readers();
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}
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}
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qemu_mutex_unlock(&rcu_gp_lock);
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qemu_mutex_unlock(&rcu_registry_lock);
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qemu_mutex_unlock(&rcu_sync_lock);
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}
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}
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@ -273,23 +292,24 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node))
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void rcu_register_thread(void)
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void rcu_register_thread(void)
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{
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{
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assert(rcu_reader.ctr == 0);
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assert(rcu_reader.ctr == 0);
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qemu_mutex_lock(&rcu_gp_lock);
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qemu_mutex_lock(&rcu_registry_lock);
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QLIST_INSERT_HEAD(®istry, &rcu_reader, node);
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QLIST_INSERT_HEAD(®istry, &rcu_reader, node);
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qemu_mutex_unlock(&rcu_gp_lock);
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qemu_mutex_unlock(&rcu_registry_lock);
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}
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}
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void rcu_unregister_thread(void)
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void rcu_unregister_thread(void)
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{
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{
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qemu_mutex_lock(&rcu_gp_lock);
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qemu_mutex_lock(&rcu_registry_lock);
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QLIST_REMOVE(&rcu_reader, node);
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QLIST_REMOVE(&rcu_reader, node);
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qemu_mutex_unlock(&rcu_gp_lock);
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qemu_mutex_unlock(&rcu_registry_lock);
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}
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}
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static void rcu_init_complete(void)
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static void rcu_init_complete(void)
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{
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{
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QemuThread thread;
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QemuThread thread;
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qemu_mutex_init(&rcu_gp_lock);
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qemu_mutex_init(&rcu_registry_lock);
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qemu_mutex_init(&rcu_sync_lock);
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qemu_event_init(&rcu_gp_event, true);
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qemu_event_init(&rcu_gp_event, true);
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qemu_event_init(&rcu_call_ready_event, false);
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qemu_event_init(&rcu_call_ready_event, false);
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@ -306,12 +326,14 @@ static void rcu_init_complete(void)
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#ifdef CONFIG_POSIX
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#ifdef CONFIG_POSIX
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static void rcu_init_lock(void)
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static void rcu_init_lock(void)
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{
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{
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qemu_mutex_lock(&rcu_gp_lock);
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qemu_mutex_lock(&rcu_sync_lock);
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qemu_mutex_lock(&rcu_registry_lock);
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}
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}
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static void rcu_init_unlock(void)
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static void rcu_init_unlock(void)
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{
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{
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qemu_mutex_unlock(&rcu_gp_lock);
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qemu_mutex_unlock(&rcu_registry_lock);
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qemu_mutex_unlock(&rcu_sync_lock);
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}
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}
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#endif
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#endif
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