Commit afbe70535ff1a8a7a32910cc15ebecc0ba92e7da introduced the function
qemu_mutex_iothread_locked to avoid recursive locking of the iothread
lock. The iothread_locked variable uses the __thread attribute which
results in a per thread storage location whereas the qemu_global_mutex
is not thread specific. This leads to race conditions because the
variable is not in sync between threads. I triggered this problem
reproducible on a Windows machine whereas Linux works fine.
After removing the __thread attribute, iothread_locked may still return
an invalid state because some functions directly use qemu_cond_wait
which will unlock and lock the qemu_global_mutex based on a condition.
These calls must be synced with iothread_locked as well.
The patch removes the __thread flag from iothread_locked and adds a
function called qemu_cond_wait_iothread to keep iothread_locked in sync.
Signed-off-by: David Engraf <david.eng...@sysgo.com>
---
cpus.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
diff --git a/cpus.c b/cpus.c
index 877bd70..d7cdd11 100644
--- a/cpus.c
+++ b/cpus.c
@@ -70,6 +70,8 @@ static CPUState *next_cpu;
int64_t max_delay;
int64_t max_advance;
+static void qemu_cond_wait_iothread(QemuCond *cond);
+
/* vcpu throttling controls */
static QEMUTimer *throttle_timer;
static unsigned int throttle_percentage;
@@ -920,7 +922,7 @@ void run_on_cpu(CPUState *cpu, void (*func)(void
*data), void *data)
while (!atomic_mb_read(&wi.done)) {
CPUState *self_cpu = current_cpu;
- qemu_cond_wait(&qemu_work_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_work_cond);
current_cpu = self_cpu;
}
}
@@ -998,11 +1000,11 @@ static void qemu_tcg_wait_io_event(CPUState *cpu)
/* Start accounting real time to the virtual clock if the CPUs
are idle. */
qemu_clock_warp(QEMU_CLOCK_VIRTUAL);
- qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(cpu->halt_cond);
}
while (iothread_requesting_mutex) {
- qemu_cond_wait(&qemu_io_proceeded_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_io_proceeded_cond);
}
CPU_FOREACH(cpu) {
@@ -1013,7 +1015,7 @@ static void qemu_tcg_wait_io_event(CPUState *cpu)
static void qemu_kvm_wait_io_event(CPUState *cpu)
{
while (cpu_thread_is_idle(cpu)) {
- qemu_cond_wait(cpu->halt_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(cpu->halt_cond);
}
qemu_kvm_eat_signals(cpu);
@@ -1123,7 +1125,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
/* wait for initial kick-off after machine start */
while (first_cpu->stopped) {
- qemu_cond_wait(first_cpu->halt_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(first_cpu->halt_cond);
/* process any pending work */
CPU_FOREACH(cpu) {
@@ -1208,13 +1210,20 @@ bool qemu_in_vcpu_thread(void)
return current_cpu && qemu_cpu_is_self(current_cpu);
}
-static __thread bool iothread_locked = false;
+static bool iothread_locked;
bool qemu_mutex_iothread_locked(void)
{
return iothread_locked;
}
+static void qemu_cond_wait_iothread(QemuCond *cond)
+{
+ iothread_locked = false;
+ qemu_cond_wait(cond, &qemu_global_mutex);
+ iothread_locked = true;
+}
+
void qemu_mutex_lock_iothread(void)
{
atomic_inc(&iothread_requesting_mutex);
@@ -1277,7 +1286,7 @@ void pause_all_vcpus(void)
}
while (!all_vcpus_paused()) {
- qemu_cond_wait(&qemu_pause_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_pause_cond);
CPU_FOREACH(cpu) {
qemu_cpu_kick(cpu);
}
@@ -1326,7 +1335,7 @@ static void qemu_tcg_init_vcpu(CPUState *cpu)
cpu->hThread = qemu_thread_get_handle(cpu->thread);
#endif
while (!cpu->created) {
- qemu_cond_wait(&qemu_cpu_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_cpu_cond);
}
tcg_cpu_thread = cpu->thread;
} else {
@@ -1347,7 +1356,7 @@ static void qemu_kvm_start_vcpu(CPUState *cpu)
qemu_thread_create(cpu->thread, thread_name, qemu_kvm_cpu_thread_fn,
cpu, QEMU_THREAD_JOINABLE);
while (!cpu->created) {
- qemu_cond_wait(&qemu_cpu_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_cpu_cond);
}
}
@@ -1363,7 +1372,7 @@ static void qemu_dummy_start_vcpu(CPUState *cpu)
qemu_thread_create(cpu->thread, thread_name,
qemu_dummy_cpu_thread_fn, cpu,
QEMU_THREAD_JOINABLE);
while (!cpu->created) {
- qemu_cond_wait(&qemu_cpu_cond, &qemu_global_mutex);
+ qemu_cond_wait_iothread(&qemu_cpu_cond);
}
}
--
1.9.1
