commit 2a96a552f9502ac34c29da2f3a39788db5ee5692
author Paolo Bonzini <pbonzini@redhat.com> Fri Mar 25 14:00:51 2016 +0100
committer Paolo Bonzini <pbonzini@redhat.com> Tue Aug 08 10:40:19 2017 +0200
tree e42372e2e5b2f73900092848f19463e9f0a7441d
parent 73c6e4013b4cd92d3d531bc22cc29e6036ef42e0

Revert "rcu: do not create thread in pthread_atfork callback"

This reverts commit a59629fcc6f603e19b516dc08f75334e5c480bd0.
This is not needed anymore because the IOThread mutex is not
"magic" anymore (need not kick the CPU thread)and also because
fork callbacks are only enabled at the very beginning of
QEMU's execution.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/rcu.h

diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h
index c0da990..f19413d 100644
--- a/include/qemu/rcu.h
+++ b/include/qemu/rcu.h
@@ -111,7 +111,6 @@
  */
 extern void rcu_enable_atfork(void);
 extern void rcu_disable_atfork(void);
-extern void rcu_after_fork(void);
 
 struct rcu_head;
 typedef void RCUCBFunc(struct rcu_head *head);

linux-user/syscall.c

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 54343c0..9b6364a 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6354,7 +6354,6 @@
         ret = fork();
         if (ret == 0) {
             /* Child Process.  */
-            rcu_after_fork();
             cpu_clone_regs(env, newsp);
             fork_end(1);
             /* There is a race condition here.  The parent process could

os-posix.c

diff --git a/os-posix.c b/os-posix.c
index c6ddb7d..92e9d85 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -34,7 +34,6 @@
 #include "sysemu/sysemu.h"
 #include "net/slirp.h"
 #include "qemu-options.h"
-#include "qemu/rcu.h"
 #include "qemu/error-report.h"
 #include "qemu/log.h"
 #include "qemu/cutils.h"
@@ -249,7 +248,6 @@
         signal(SIGTSTP, SIG_IGN);
         signal(SIGTTOU, SIG_IGN);
         signal(SIGTTIN, SIG_IGN);
-        rcu_after_fork();
     }
 }
 

util/rcu.c

diff --git a/util/rcu.c b/util/rcu.c
index 2142ddd..ca5a63e 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -350,18 +350,22 @@
     qemu_mutex_unlock(&rcu_registry_lock);
     qemu_mutex_unlock(&rcu_sync_lock);
 }
-#endif
 
-void rcu_after_fork(void)
+static void rcu_init_child(void)
 {
+    if (atfork_depth < 1) {
+        return;
+    }
+
     memset(&registry, 0, sizeof(registry));
     rcu_init_complete();
 }
+#endif
 
 static void __attribute__((__constructor__)) rcu_init(void)
 {
 #ifdef CONFIG_POSIX
-    pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_unlock);
+    pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
 #endif
     rcu_init_complete();
 }