On 2011-02-01 13:47, Marcelo Tosatti wrote:
> On Thu, Jan 27, 2011 at 02:09:58PM +0100, Jan Kiszka wrote:
>> Found by Stefan Hajnoczi: There is a race in kvm_cpu_exec between
>> checking for exit_request on vcpu entry and timer signals arriving
>> before KVM starts to catch them. Plug it by blocking both timer related
>> signals also on !CONFIG_IOTHREAD and process those via signalfd.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>> CC: Stefan Hajnoczi <stefanha@xxxxxxxxxxxxxxxxxx>
>> ---
>> cpus.c | 18 ++++++++++++++++++
>> 1 files changed, 18 insertions(+), 0 deletions(-)
>>
>> diff --git a/cpus.c b/cpus.c
>> index fc3f222..29b1070 100644
>> --- a/cpus.c
>> +++ b/cpus.c
>> @@ -254,6 +254,10 @@ static void qemu_kvm_init_cpu_signals(CPUState *env)
>> pthread_sigmask(SIG_BLOCK, NULL, &set);
>> sigdelset(&set, SIG_IPI);
>> sigdelset(&set, SIGBUS);
>> +#ifndef CONFIG_IOTHREAD
>> + sigdelset(&set, SIGIO);
>> + sigdelset(&set, SIGALRM);
>> +#endif
>
> I'd prefer separate qemu_kvm_init_cpu_signals in the !IOTHREAD
> section.
You mean to duplicate qemu_kvm_init_cpu_signals for both configurations?
>
>> r = kvm_set_signal_mask(env, &set);
>> if (r) {
>> fprintf(stderr, "kvm_set_signal_mask: %s\n", strerror(-r));
>> @@ -351,6 +355,12 @@ static void qemu_kvm_eat_signals(CPUState *env)
>> exit(1);
>> }
>> } while (sigismember(&chkset, SIG_IPI) || sigismember(&chkset, SIGBUS));
>> +
>> +#ifndef CONFIG_IOTHREAD
>> + if (sigismember(&chkset, SIGIO) || sigismember(&chkset, SIGALRM)) {
>> + qemu_notify_event();
>> + }
>> +#endif
>
> Why is this necessary?
>
> You should break out of cpu_exec_all if there's a pending alarm (see
> qemu_alarm_pending()).
qemu_alarm_pending() is not true until the signal is actually taken. The
alarm handler sets the required flags.
>
>> }
>>
>> #else /* _WIN32 */
>> @@ -398,6 +408,14 @@ int qemu_init_main_loop(void)
>> int ret;
>>
>> sigemptyset(&blocked_signals);
>> + if (kvm_enabled()) {
>> + /*
>> + * We need to process timer signals synchronously to avoid a race
>> + * between exit_request check and KVM vcpu entry.
>> + */
>> + sigaddset(&blocked_signals, SIGIO);
>> + sigaddset(&blocked_signals, SIGALRM);
>> + }
>
> A block_io_signals() function for !IOTHREAD would be nicer.
Well, we aren't blocking all I/O signals, so I decided against causing
confusion to people that try to compare the result against real
block_io_signals. If you mean just pushing those lines that set up
blocked_signals into a separate function, then I need to find a good
name for it.
>
>>
>> ret = qemu_signalfd_init(blocked_signals);
>> if (ret) {
>> --
>> 1.7.1
Thanks,
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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