On 21/09/2016 18:15, Emilio G. Cota wrote:
> On Mon, Sep 19, 2016 at 14:50:56 +0200, Paolo Bonzini wrote:
>> It is not necessary to hold qemu_cpu_list_mutex throughout the
>> exclusive section, because no other exclusive section can run
>> while pending_cpus != 0.
>>
>> exclusive_idle() is called in cpu_exec_start(), and that prevents
>> any CPUs created after start_exclusive() from entering cpu_exec()
>> during an exclusive section.
>>
>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>> ---
>> cpus-common.c | 6 ++++++
>> docs/tcg-exclusive.promela | 4 +++-
>> include/qom/cpu.h | 4 ----
>> 3 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/cpus-common.c b/cpus-common.c
>> index 9225c65..6adc982 100644
>> --- a/cpus-common.c
>> +++ b/cpus-common.c
>> @@ -191,11 +191,17 @@ void start_exclusive(void)
>> if (pending_cpus > 1) {
>> qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_mutex);
>> }
>> +
>> + /* Can release mutex, no one will enter another exclusive
>> + * section until end_exclusive resets pending_cpus to 0.
>> + */
>> + qemu_mutex_unlock(&qemu_cpu_list_mutex);
>> }
>>
>> /* Finish an exclusive operation. Releases qemu_cpu_list_mutex. */
>> void end_exclusive(void)
>> {
>> + qemu_mutex_lock(&qemu_cpu_list_mutex);
>> pending_cpus = 0;
>> qemu_cond_broadcast(&exclusive_resume);
>> qemu_mutex_unlock(&qemu_cpu_list_mutex);
>
> The comments at the top of both start_exclusive and end_exclusive
> should be updated.
>
> E.
>
Ok.
Paolo
