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[Qemu-devel] [PATCH v2 14/22] kvm: Fix race between timer signals and vc
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] [PATCH v2 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD |
Date: |
Thu, 27 Jan 2011 15:20:15 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
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 <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
---
Added blocking of SIGIO/SIGALRM which was missing in previous version.
Stefan just provided a test case, and that now passes.
However, I realized (and checked) that this fix does not work with
signalfd_compat: The signals will be swallowed by the helper thread.
That affects all host kernels < 2.6.22. Given that we require 2.6.29 as
baseline (unless kvm-kmod is used) and that !CONFIG_IOTHREAD is not that
important for KVM mode, I tend to catch and reject
CONFIG_KVM+!CONFIG_IOTHREAD+!CONFIG_SIGNALFD as unsupported during
configure. Comments?
cpus.c | 20 ++++++++++++++++++++
1 files changed, 20 insertions(+), 0 deletions(-)
diff --git a/cpus.c b/cpus.c
index fc3f222..f9d9f9e 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
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
}
#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);
+ }
ret = qemu_signalfd_init(blocked_signals);
if (ret) {
@@ -535,6 +553,8 @@ static sigset_t block_io_signals(void)
sigaddset(&set, SIGALRM);
sigaddset(&set, SIG_IPI);
sigaddset(&set, SIGBUS);
+ sigaddset(&set, SIGIO);
+ sigaddset(&set, SIGALRM);
pthread_sigmask(SIG_BLOCK, &set, NULL);
memset(&action, 0, sizeof(action));
--
1.7.1
- [Qemu-devel] [PATCH 00/22] [uq/master] Patch queue, part II, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 03/22] Process vmstop requests in IO thread, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 21/22] Refactor kvm&tcg function names in cpus.c, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 10/22] kvm: Set up signal mask also for !CONFIG_IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 18/22] kvm: Unconditionally reenter kernel after IO exits, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH v2 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD,
Jan Kiszka <=
- [Qemu-devel] [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Stefan Hajnoczi, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Stefan Hajnoczi, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
[Qemu-devel] [PATCH 04/22] Leave inner main_loop faster on pending requests, Jan Kiszka, 2011/01/27