linux-kernel - [PATCH 5.12 129/677] KVM: selftests: Always run vCPU thread with blocked SIG

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Date:   Wed, 12 May 2021 16:42:55 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.12 129/677] KVM: selftests: Always run vCPU thread with blocked SIG_IPI

From: Paolo Bonzini <pbonzini@...hat.com>

commit bf1e15a82e3b74ee86bb119d6038b41e1ed2b319 upstream.

The main thread could start to send SIG_IPI at any time, even before signal
blocked on vcpu thread.  Therefore, start the vcpu thread with the signal
blocked.

Without this patch, on very busy cores the dirty_log_test could fail directly
on receiving a SIGUSR1 without a handler (when vcpu runs far slower than main).

Reported-by: Peter Xu <peterx@...hat.com>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/testing/selftests/kvm/dirty_log_test.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -527,9 +527,8 @@ static void *vcpu_worker(void *data)
 	 */
 	sigmask->len = 8;
 	pthread_sigmask(0, NULL, sigset);
+	sigdelset(sigset, SIG_IPI);
 	vcpu_ioctl(vm, VCPU_ID, KVM_SET_SIGNAL_MASK, sigmask);
-	sigaddset(sigset, SIG_IPI);
-	pthread_sigmask(SIG_BLOCK, sigset, NULL);
 
 	sigemptyset(sigset);
 	sigaddset(sigset, SIG_IPI);
@@ -858,6 +857,7 @@ int main(int argc, char *argv[])
 		.interval = TEST_HOST_LOOP_INTERVAL,
 	};
 	int opt, i;
+	sigset_t sigset;
 
 	sem_init(&sem_vcpu_stop, 0, 0);
 	sem_init(&sem_vcpu_cont, 0, 0);
@@ -916,6 +916,11 @@ int main(int argc, char *argv[])
 
 	srandom(time(0));
 
+	/* Ensure that vCPU threads start with SIG_IPI blocked.  */
+	sigemptyset(&sigset);
+	sigaddset(&sigset, SIG_IPI);
+	pthread_sigmask(SIG_BLOCK, &sigset, NULL);
+
 	if (host_log_mode_option == LOG_MODE_ALL) {
 		/* Run each log mode */
 		for (i = 0; i < LOG_MODE_NUM; i++) {