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[Qemu-devel] [PATCH 16/23] kvm: Fix race between timer signals and vcpu
From: |
Marcelo Tosatti |
Subject: |
[Qemu-devel] [PATCH 16/23] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD |
Date: |
Fri, 4 Feb 2011 13:47:19 -0200 |
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>
Signed-off-by: Marcelo Tosatti <address@hidden>
---
configure | 6 ++++++
cpus.c | 31 ++++++++++++++++++++++++++++++-
2 files changed, 36 insertions(+), 1 deletions(-)
diff --git a/configure b/configure
index 598e8e1..a3f5345 100755
--- a/configure
+++ b/configure
@@ -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
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) {
--
1.7.2.3
- [Qemu-devel] [PATCH 19/23] kvm: Unconditionally reenter kernel after IO exits, (continued)
- [Qemu-devel] [PATCH 19/23] kvm: Unconditionally reenter kernel after IO exits, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 18/23] Introduce VCPU self-signaling service, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 07/23] kvm: Report proper error on GET_VCPU_MMAP_SIZE failures, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 23/23] kvm: make tsc stable over migration and machine start, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 13/23] kvm: Refactor qemu_kvm_eat_signals, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 21/23] kvm: Leave kvm_cpu_exec directly after KVM_EXIT_SHUTDOWN, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 22/23] x86: Fix MCA broadcast parameters for TCG case, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 08/23] kvm: Drop redundant kvm_enabled from kvm_cpu_thread_fn, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 16/23] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD,
Marcelo Tosatti <=
- [Qemu-devel] [PATCH 02/23] Stop current VCPU on synchronous reset requests, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 05/23] Leave inner main_loop faster on pending requests, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 20/23] kvm: Remove static return code of kvm_handle_io, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 10/23] kvm: Provide sigbus services arch-independently, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 15/23] Set up signalfd under !CONFIG_IOTHREAD, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 12/23] kvm: Set up signal mask also for !CONFIG_IOTHREAD, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 06/23] Flatten the main loop, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 01/23] Prevent abortion on multiple VCPU kicks, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 04/23] Trigger exit from cpu_exec_all on pending IO events, Marcelo Tosatti, 2011/02/04
- [Qemu-devel] [PATCH 14/23] kvm: Call qemu_kvm_eat_signals also under !CONFIG_IOTHREAD, Marcelo Tosatti, 2011/02/04