@@ -37,6 +37,7 @@
#include "sysemu/qtest.h"
#include "qemu/main-loop.h"
#include "qemu/bitmap.h"
+#include "qemu/seqlock.h"
#ifndef _WIN32
#include "qemu/compatfd.h"
@@ -107,6 +108,13 @@ static int64_t qemu_icount;
typedef struct TimersState {
int64_t cpu_ticks_prev;
int64_t cpu_ticks_offset;
+ /* cpu_clock_offset will be read out of BQL, so protect it with private
+ * lock. As for cpu_ticks_*, no requirement to read it outside BQL yet.
+ * Lock rule: innermost
+ */
+ QemuSeqLock clock_seqlock;
+ /* mutex for seqlock */
+ QemuMutex mutex;
int64_t cpu_clock_offset;
int32_t cpu_ticks_enabled;
int64_t dummy;
@@ -132,6 +140,7 @@ int64_t cpu_get_icount(void)
}
/* return the host CPU cycle counter and handle stop/restart */
+/* cpu_ticks is safely if holding BQL */
int64_t cpu_get_ticks(void)
{
if (use_icount) {
@@ -156,33 +165,46 @@ int64_t cpu_get_ticks(void)
int64_t cpu_get_clock(void)
{
int64_t ti;
- if (!timers_state.cpu_ticks_enabled) {
- return timers_state.cpu_clock_offset;
- } else {
- ti = get_clock();
- return ti + timers_state.cpu_clock_offset;
- }
+ unsigned start;
+
+ do {
+ start = seqlock_read_begin(&timers_state.clock_seqlock);
+ if (!timers_state.cpu_ticks_enabled) {
+ ti = timers_state.cpu_clock_offset;
+ } else {
+ ti = get_clock();
+ ti += timers_state.cpu_clock_offset;
+ }
+ } while (seqlock_read_check(&timers_state.clock_seqlock, start));
+
+ return ti;
}
/* enable cpu_get_ticks() */
void cpu_enable_ticks(void)
{
+ /* Here, the really thing protected by seqlock is cpu_clock_offset. */
+ seqlock_write_lock(&timers_state.clock_seqlock);
if (!timers_state.cpu_ticks_enabled) {
timers_state.cpu_ticks_offset -= cpu_get_real_ticks();
timers_state.cpu_clock_offset -= get_clock();
timers_state.cpu_ticks_enabled = 1;
}
+ seqlock_write_unlock(&timers_state.clock_seqlock);
}
/* disable cpu_get_ticks() : the clock is stopped. You must not call
cpu_get_ticks() after that. */
void cpu_disable_ticks(void)
{
+ /* Here, the really thing protected by seqlock is cpu_clock_offset. */
+ seqlock_write_lock(&timers_state.clock_seqlock);
if (timers_state.cpu_ticks_enabled) {
timers_state.cpu_ticks_offset = cpu_get_ticks();
timers_state.cpu_clock_offset = cpu_get_clock();
timers_state.cpu_ticks_enabled = 0;
}
+ seqlock_write_unlock(&timers_state.clock_seqlock);
}
/* Correlation between real and virtual time is always going to be
@@ -366,6 +388,8 @@ static const VMStateDescription vmstate_timers = {
void configure_icount(const char *option)
{
+ qemu_mutex_init(&timers_state.mutex);
+ seqlock_init(&timers_state.clock_seqlock, &timers_state.mutex);
vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
if (!option) {
return;
The vm_clock may be read outside BQL. This will make timers_state --the foundation of vm_clock exposed to race condition. Using private lock to protect it. Note in tcg mode, vm_clock still read inside BQL, so icount is left without private lock's protection. As for cpu_ticks_* in timers_state, it is still protected by BQL. Lock rule: private lock innermost, ie BQL->"this lock" Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> --- cpus.c | 36 ++++++++++++++++++++++++++++++------ 1 file changed, 30 insertions(+), 6 deletions(-)