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kvm: Fix race between timer signals and vcpu entry under !IOTHREAD 

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.

As this fix depends on real signalfd support (otherwise the timer
signals only kick the compat helper thread, and the main thread hangs),
we need to detect the invalid constellation and abort configure.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
CC: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Jan Kiszka 2011-02-01 22:15:57 +01:00 committed by Marcelo Tosatti
parent d0f294cec0
commit de758970b6
2 changed files with 36 additions and 1 deletions
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6
configure vendored
View File

@ -2057,6 +2057,12 @@ EOF
if compile_prog "" "" ; then
signalfd=yes
elif test "$kvm" = "yes" -a "$io_thread" != "yes"; then
echo
echo "ERROR: Host kernel lacks signalfd() support,"
echo "but KVM depends on it when the IO thread is disabled."
echo
exit 1
fi
# check if eventfd is supported

31
cpus.c
View File

@ -319,6 +319,12 @@ 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
}
#else /* _WIN32 */
@ -368,11 +374,15 @@ static void qemu_kvm_init_cpu_signals(CPUState *env)
sigemptyset(&set);
sigaddset(&set, SIG_IPI);
sigaddset(&set, SIGIO);
sigaddset(&set, SIGALRM);
pthread_sigmask(SIG_BLOCK, &set, NULL);
pthread_sigmask(SIG_BLOCK, NULL, &set);
sigdelset(&set, SIG_IPI);
sigdelset(&set, SIGBUS);
sigdelset(&set, SIGIO);
sigdelset(&set, SIGALRM);
r = kvm_set_signal_mask(env, &set);
if (r) {
fprintf(stderr, "kvm_set_signal_mask: %s\n", strerror(-r));
@ -381,13 +391,32 @@ static void qemu_kvm_init_cpu_signals(CPUState *env)
#endif
}
#ifndef _WIN32
static sigset_t block_synchronous_signals(void)
{
sigset_t set;
sigemptyset(&set);
if (kvm_enabled()) {
/*
* We need to process timer signals synchronously to avoid a race
* between exit_request check and KVM vcpu entry.
*/
sigaddset(&set, SIGIO);
sigaddset(&set, SIGALRM);
}
return set;
}
#endif
int qemu_init_main_loop(void)
{
#ifndef _WIN32
sigset_t blocked_signals;
int ret;
sigemptyset(&blocked_signals);
blocked_signals = block_synchronous_signals();
ret = qemu_signalfd_init(blocked_signals);
if (ret) {