On 2013-07-21 10:43, Liu Ping Fan wrote:
> In kvm mode, vm_clock may be read on AioContexts outside BQL(next
> patch). 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 change.
>
> Lock rule: private lock innermost, ie BQL->"this lock"
>
> Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
> ---
> cpus.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 4254ca9..22df5fb 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -113,6 +113,8 @@ typedef struct TimersState {
> } TimersState;
>
> static TimersState timers_state;
> +/* lock rule: innermost */
> +static QemuMutex timers_state_lock;
>
> /* Return the virtual CPU time, based on the instruction counter. */
> int64_t cpu_get_icount(void)
> @@ -134,11 +136,15 @@ int64_t cpu_get_icount(void)
> /* return the host CPU cycle counter and handle stop/restart */
> int64_t cpu_get_ticks(void)
> {
> + int64_t ret;
> +
> if (use_icount) {
[ Some day we should introduce something like assert_bql_held() and add
it here, among other places. ]
> return cpu_get_icount();
> }
> + qemu_mutex_lock(&timers_state_lock);
> if (!timers_state.cpu_ticks_enabled) {
> - return timers_state.cpu_ticks_offset;
> + ret = timers_state.cpu_ticks_offset;
> + goto out;
No need for goto here and below.
> } else {
> int64_t ticks;
> ticks = cpu_get_real_ticks();
> @@ -148,41 +154,53 @@ int64_t cpu_get_ticks(void)
> timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev -
> ticks;
> }
> timers_state.cpu_ticks_prev = ticks;
> - return ticks + timers_state.cpu_ticks_offset;
> + ret = ticks + timers_state.cpu_ticks_offset;
> + goto out;
> }
> +out:
> + qemu_mutex_lock(&timers_state_lock);
> + return ret;
> }
>
> /* return the host CPU monotonic timer and handle stop/restart */
> int64_t cpu_get_clock(void)
> {
> int64_t ti;
> +
> + qemu_mutex_lock(&timers_state_lock);
> if (!timers_state.cpu_ticks_enabled) {
> - return timers_state.cpu_clock_offset;
> + ti = timers_state.cpu_clock_offset;
> } else {
> ti = get_clock();
> - return ti + timers_state.cpu_clock_offset;
> + ti += timers_state.cpu_clock_offset;
> }
> + qemu_mutex_unlock(&timers_state_lock);
> + return ti;
> }
>
> /* enable cpu_get_ticks() */
> void cpu_enable_ticks(void)
> {
> + qemu_mutex_lock(&timers_state_lock);
> 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;
> }
> + qemu_mutex_unlock(&timers_state_lock);
> }
>
> /* disable cpu_get_ticks() : the clock is stopped. You must not call
> cpu_get_ticks() after that. */
> void cpu_disable_ticks(void)
> {
> + qemu_mutex_lock(&timers_state_lock);
> 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;
> }
> + qemu_mutex_unlock(&timers_state_lock);
> }
>
> /* Correlation between real and virtual time is always going to be
> @@ -353,6 +371,7 @@ static const VMStateDescription vmstate_timers = {
>
> void configure_icount(const char *option)
[ Misnamed function, it's not only about icount stuff - but not an issue
of this patch. ]
> {
> + qemu_mutex_init(&timers_state_lock);
> vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
> if (!option) {
> return;
>
Looks good except for the goto.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
