From mboxrd@z Thu Jan  1 00:00:00 1970
From: Balbir Singh <bsingharora@gmail.com>
Subject: [KVMTOOL][PATCH 4/5] Fix a race during exit processing
Date: Sun,  3 Apr 2016 20:38:01 +1000
Message-ID: <1459679882-30382-5-git-send-email-bsingharora@gmail.com>
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Cc: mpe@ellerman.id.au, mikey@neuling.org, aik@ozlabs.ru,
	Balbir Singh <bsingharora@gmail.com>
To: will.deacon@arm.com, kvm@vger.kernel.org
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Fix a race, described below

	lkvm stop ...	handle_stop
			kvm_cpu__reboot
			kvm_cmd_run_exit
			vcpus exit
			...
			dev_exit
			...
			ioport__unregister
			..serial...
			kvm__pause --> br_write_lock
			pthread_kill

But the thread is already dead above.

We mark the cpus as dying so that kvm_pause does nothing.
This should not break any semantics

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
---
 builtin-run.c | 3 +++
 kvm.c         | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/builtin-run.c b/builtin-run.c
index 17b1428..cdc7158 100644
--- a/builtin-run.c
+++ b/builtin-run.c
@@ -58,6 +58,7 @@ __thread struct kvm_cpu *current_kvm_cpu;
 static int  kvm_run_wrapper;
 
 bool do_debug_print = false;
+int kvm_cmd_exit;
 
 static const char * const run_usage[] = {
 	"lkvm run [<options>] [<kernel image>]",
@@ -648,6 +649,7 @@ static void kvm_cmd_run_exit(struct kvm *kvm, int guest_ret)
 {
 	compat__print_all_messages();
 
+	kvm_cmd_exit = 1;
 	init_list__exit(kvm);
 
 	if (guest_ret == 0 && do_debug_print)
@@ -659,6 +661,7 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 	int ret = -EFAULT;
 	struct kvm *kvm;
 
+	kvm_cmd_exit = 0;
 	kvm = kvm_cmd_run_init(argc, argv);
 	if (IS_ERR(kvm))
 		return PTR_ERR(kvm);
diff --git a/kvm.c b/kvm.c
index 1081072..53cf0e2 100644
--- a/kvm.c
+++ b/kvm.c
@@ -33,6 +33,8 @@
 
 #define DEFINE_KVM_EXIT_REASON(reason) [reason] = #reason
 
+extern int kvm_cmd_exit;
+
 const char *kvm_exit_reasons[] = {
 	DEFINE_KVM_EXIT_REASON(KVM_EXIT_UNKNOWN),
 	DEFINE_KVM_EXIT_REASON(KVM_EXIT_EXCEPTION),
@@ -435,6 +437,9 @@ void kvm__pause(struct kvm *kvm)
 	if (!kvm->cpus[0] || kvm->cpus[0]->thread == 0)
 		return;
 
+	if (kvm_cmd_exit)
+		return;
+
 	mutex_lock(&pause_lock);
 
 	pause_event = eventfd(0, 0);
-- 
2.5.5