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[Qemu-devel] [PATCH for-2.11] rcu: init globals only once
From: |
Peter Xu |
Subject: |
[Qemu-devel] [PATCH for-2.11] rcu: init globals only once |
Date: |
Tue, 8 Aug 2017 15:00:07 +0800 |
We were calling rcu_init_complete() twice in the child processes when
fork happened. However the pthread library does not really suggest to do
it that way:
http://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_mutex_init.html
"Attempting to initialise an already initialised mutex results in
undefined behaviour."
Actually, IMHO we can do it in a more natural way: Firstly, we only init
the RCU globals once in rcu_init(). Then, in rcu_init_child(), we unlock
all the locks held in rcu_init_lock() just like what we do in the parent
process, then do the rest of RCU re-init (e.g., create the RCU thread).
CC: Paolo Bonzini <address@hidden>
Signed-off-by: Peter Xu <address@hidden>
---
this is based on Paolo's series:
"[PATCH for-2.10 0/2] RCU: forking fix and cleanups"
---
util/rcu.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/util/rcu.c b/util/rcu.c
index ca5a63e..6fbbe4c 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -299,15 +299,17 @@ void rcu_unregister_thread(void)
qemu_mutex_unlock(&rcu_registry_lock);
}
-static void rcu_init_complete(void)
+static void rcu_init_globals(void)
{
- QemuThread thread;
-
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);
+}
+
+static void rcu_init_complete(void)
+{
+ QemuThread thread;
/* The caller is assumed to have iothread lock, so the call_rcu thread
* must have been quiescent even after forking, just recreate it.
@@ -357,6 +359,13 @@ static void rcu_init_child(void)
return;
}
+ rcu_init_unlock();
+
+ /*
+ * For the newly forked child, we need something extra: since
+ * after fork the threads are all gone, we need to re-init the RCU
+ * thread, along with the globals.
+ */
memset(®istry, 0, sizeof(registry));
rcu_init_complete();
}
@@ -367,5 +376,6 @@ static void __attribute__((__constructor__)) rcu_init(void)
#ifdef CONFIG_POSIX
pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
#endif
+ rcu_init_globals();
rcu_init_complete();
}
--
2.7.4
- [Qemu-devel] [PATCH for-2.11] rcu: init globals only once,
Peter Xu <=