Signed-off-by: Emilio G. Cota <c...@braap.org>
---
cpu-exec.c | 1 +
include/exec/exec-all.h | 5 +++
linux-user/main.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++
linux-user/syscall.c | 1 +
4 files changed, 96 insertions(+)
diff --git a/cpu-exec.c b/cpu-exec.c
index 63d739a..8f1adc4 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -649,6 +649,7 @@ int cpu_exec(CPUState *cpu)
g_assert(cc == CPU_GET_CLASS(cpu));
#endif /* buggy compiler */
cpu->can_do_io = 1;
+ stop_the_world_reset();
tb_lock_reset();
}
} /* for(;;) */
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index ec72c5a..c483d80 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -61,6 +61,11 @@ void QEMU_NORETURN cpu_loop_exit(CPUState *cpu);
void QEMU_NORETURN cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc);
void QEMU_NORETURN cpu_loop_exit_atomic(CPUState *cpu, uintptr_t pc);
+void stop_the_world_lock(CPUState *cpu);
+void stop_the_world_unlock(void);
+void stop_the_world_reset(void);
+extern __thread bool stw_held;
+
#if !defined(CONFIG_USER_ONLY)
void cpu_reloading_memory_map(void);
/**
diff --git a/linux-user/main.c b/linux-user/main.c
index 9880505..94c6625 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -114,11 +114,19 @@ static pthread_cond_t exclusive_cond =
PTHREAD_COND_INITIALIZER;
static pthread_cond_t exclusive_resume = PTHREAD_COND_INITIALIZER;
static int pending_cpus;
+static pthread_cond_t stw_sleep_cond = PTHREAD_COND_INITIALIZER;
+static pthread_cond_t stw_request_cond = PTHREAD_COND_INITIALIZER;
+static pthread_mutex_t stw_lock = PTHREAD_MUTEX_INITIALIZER;
+static int stw_requests;
+static bool stw_ongoing;
+__thread bool stw_held;
+
/* Make sure everything is in a consistent state for calling fork(). */
void fork_start(void)
{
qemu_mutex_lock(&tcg_ctx.tb_ctx.tb_lock);
pthread_mutex_lock(&exclusive_lock);
+ pthread_mutex_lock(&stw_lock);
mmap_fork_start();
}
@@ -137,11 +145,17 @@ void fork_end(int child)
pending_cpus = 0;
pthread_mutex_init(&exclusive_lock, NULL);
pthread_mutex_init(&cpu_list_mutex, NULL);
+ pthread_mutex_init(&stw_lock, NULL);
+ stw_held = false;
+ stw_ongoing = false;
pthread_cond_init(&exclusive_cond, NULL);
pthread_cond_init(&exclusive_resume, NULL);
+ pthread_cond_init(&stw_sleep_cond, NULL);
+ pthread_cond_init(&stw_request_cond, NULL);
qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
gdbserver_fork(thread_cpu);
} else {
+ pthread_mutex_unlock(&stw_lock);
pthread_mutex_unlock(&exclusive_lock);
qemu_mutex_unlock(&tcg_ctx.tb_ctx.tb_lock);
}
@@ -198,6 +212,79 @@ static void step_atomic(CPUState *cpu)
end_exclusive();
}
+void stop_the_world_lock(CPUState *cpu)
+{
+ CPUState *other;
+
+ if (stw_held) {
+ return;
+ }
+ rcu_read_unlock();
+ assert(!rcu_read_lock_held());
+
+ pthread_mutex_lock(&stw_lock);
+ if (stw_ongoing) {
+ stw_requests++;
+ /* wait for ongoing stops to occur */
+ while (stw_ongoing) {
+ pthread_cond_wait(&stw_request_cond, &stw_lock);
+ }
+ stw_requests--;
+ }
+
+ /* it's our turn! */
+ stw_ongoing = true;
+ stw_held = true;
+ CPU_FOREACH(other) {
+ if (other != cpu) {
+ cpu_exit(other);
+ }
+ }
+ synchronize_rcu();
+}
+
+void stop_the_world_unlock(void)
+{
+ if (!stw_held) {
+ return;
+ }
+ assert(stw_ongoing);
+ assert(!rcu_read_lock_held());
+
+ if (stw_requests) {
+ pthread_cond_signal(&stw_request_cond);
+ } else {
+ pthread_cond_broadcast(&stw_sleep_cond);
+ }
+ /*
+ * Make sure the next STW requester (if any) will perceive that we're
+ * in an RCU read critical section
+ */
+ rcu_read_lock();
+ stw_ongoing = false;
+ stw_held = false;
+ pthread_mutex_unlock(&stw_lock);
+}
+
+void stop_the_world_reset(void)
+{
+ if (likely(!stw_held)) {
+ return;
+ }
+ stop_the_world_unlock();
+}
+
+static inline void stop_the_world_sleep(void)
+{
+ pthread_mutex_lock(&stw_lock);
+ if (unlikely(stw_ongoing)) {
+ while (stw_ongoing) {
+ pthread_cond_wait(&stw_sleep_cond, &stw_lock);
+ }
+ }
+ pthread_mutex_unlock(&stw_lock);
+}
+
/* Wait for exclusive ops to finish, and begin cpu execution. */
static inline void cpu_exec_start(CPUState *cpu)
{
@@ -205,6 +292,8 @@ static inline void cpu_exec_start(CPUState *cpu)
exclusive_idle();
cpu->running = true;
pthread_mutex_unlock(&exclusive_lock);
+
+ stop_the_world_sleep();
}
/* Mark cpu as not executing, and release pending exclusive ops. */
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 2911319..740af23 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5403,6 +5403,7 @@ static void *clone_func(void *arg)
/* Wait until the parent has finshed initializing the tls state. */
pthread_mutex_lock(&clone_lock);
pthread_mutex_unlock(&clone_lock);
+ stw_held = false;
cpu_loop(env);
/* never exits */
return NULL;
--
2.5.0
