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[Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thre
From: |
Wen Congyang |
Subject: |
[Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu() |
Date: |
Tue, 28 Jul 2015 10:26:28 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
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 <address@hidden>
---
util/rcu.c | 48 +++++++++++++++++++++++++++++++++++-------------
1 file changed, 35 insertions(+), 13 deletions(-)
diff --git a/util/rcu.c b/util/rcu.c
index cdcad67..4dd33df 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -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 ®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 */
@@ -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(®istry)) {
/* 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(®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 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
--
2.4.3
- [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(),
Wen Congyang <=
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Paolo Bonzini, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Wen Congyang, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Paolo Bonzini, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Wen Congyang, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Paolo Bonzini, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Wen Congyang, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Paolo Bonzini, 2015/07/28
- Re: [Qemu-devel] [PATCH v2 for-2.5] rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu(), Wen Congyang, 2015/07/28