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[Qemu-devel] [PATCH v2 17/24] kvm: Fix race between timer signals and vc
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] [PATCH v2 17/24] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD |
Date: |
Tue, 1 Feb 2011 22:15:57 +0100 |
From: Jan Kiszka <address@hidden>
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 <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
---
configure | 6 ++++++
cpus.c | 31 ++++++++++++++++++++++++++++++-
2 files changed, 36 insertions(+), 1 deletions(-)
diff --git a/configure b/configure
index 4673bf0..368ca8a 100755
--- a/configure
+++ b/configure
@@ -2056,6 +2056,12 @@ 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
diff --git a/cpus.c b/cpus.c
index 359361f..18caf47 100644
--- a/cpus.c
+++ b/cpus.c
@@ -327,6 +327,12 @@ 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 */
@@ -376,11 +382,15 @@ 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));
@@ -389,13 +399,32 @@ 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) {
--
1.7.1
- [Qemu-devel] [PATCH v2 00/24] [uq/master] Patch queue, part II, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 11/24] kvm: Provide sigbus services arch-independently, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 04/24] Process vmstop requests in IO thread, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 23/24] Refactor kvm&tcg function names in cpus.c, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 17/24] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD,
Jan Kiszka <=
- [Qemu-devel] [PATCH v2 18/24] kvm: Add MCE signal support for !CONFIG_IOTHREAD, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 01/24] kvm: x86: Fix build in absence of KVM_CAP_ASYNC_PF, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 21/24] kvm: Remove static return code of kvm_handle_io, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 22/24] kvm: Leave kvm_cpu_exec directly after KVM_EXIT_SHUTDOWN, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 07/24] Flatten the main loop, Jan Kiszka, 2011/02/01
- [Qemu-devel] [PATCH v2 13/24] kvm: Set up signal mask also for !CONFIG_IOTHREAD, Jan Kiszka, 2011/02/01