[v2] Issue in exit timing clearance

Commit Message

Bharat Bhushan March 25, 2011, 5:02 a.m. UTC

None

Comments

Avi Kivity April 5, 2011, 9:05 a.m. UTC | #1

On 03/25/2011 07:02 AM, Bharat Bhushan wrote:
> Following dump is observed on host when clearing the exit timing counters
>
> [root@p1021mds kvm]# echo -n 'c'>  vm1200_vcpu0_timing
> INFO: task echo:1276 blocked for more than 120 seconds.
> "echo 0>  /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> echo          D 0ff5bf94     0  1276   1190 0x00000000
> Call Trace:
> [c2157e40] [c0007908] __switch_to+0x9c/0xc4
> [c2157e50] [c040293c] schedule+0x1b4/0x3bc
> [c2157e90] [c04032dc] __mutex_lock_slowpath+0x74/0xc0
> [c2157ec0] [c00369e4] kvmppc_init_timing_stats+0x20/0xb8
> [c2157ed0] [c0036b00] kvmppc_exit_timing_write+0x84/0x98
> [c2157ef0] [c00b9f90] vfs_write+0xc0/0x16c
> [c2157f10] [c00ba284] sys_write+0x4c/0x90
> [c2157f40] [c000e320] ret_from_syscall+0x0/0x3c
>
>          The vcpu->mutex is used by kvm_ioctl_* (KVM_RUN etc) and same was
> used when clearing the stats (in kvmppc_init_timing_stats()). What happens
> is that when the guest is idle then it held the vcpu->mutx. While the
> exiting timing process waits for guest to release the vcpu->mutex and
> a hang state is reached.
>
>          Now using seprate lock for exit timing stats.
>

Applied, thanks.

Patch

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index bba3b9b..890897c 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -255,6 +255,7 @@  struct kvm_vcpu_arch {
 	u32 dbsr;
 
 #ifdef CONFIG_KVM_EXIT_TIMING
+	struct mutex exit_timing_lock;
 	struct kvmppc_exit_timing timing_exit;
 	struct kvmppc_exit_timing timing_last_enter;
 	u32 last_exit_type;
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 9975846..ec3d2e7 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -284,6 +284,10 @@  int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	tasklet_init(&vcpu->arch.tasklet, kvmppc_decrementer_func, (ulong)vcpu);
 	vcpu->arch.dec_timer.function = kvmppc_decrementer_wakeup;
 
+#ifdef CONFIG_KVM_EXIT_TIMING
+	mutex_init(&vcpu->arch.exit_timing_lock);
+#endif
+
 	return 0;
 }
 
diff --git a/arch/powerpc/kvm/timing.c b/arch/powerpc/kvm/timing.c
index a021f58..18f40fd 100644
--- a/arch/powerpc/kvm/timing.c
+++ b/arch/powerpc/kvm/timing.c
@@ -34,8 +34,8 @@  void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
 {
 	int i;
 
-	/* pause guest execution to avoid concurrent updates */
-	mutex_lock(&vcpu->mutex);
+	/* Take a lock to avoid concurrent updates */
+	mutex_lock(&vcpu->arch.exit_timing_lock);
 
 	vcpu->arch.last_exit_type = 0xDEAD;
 	for (i = 0; i < __NUMBER_OF_KVM_EXIT_TYPES; i++) {
@@ -49,7 +49,7 @@  void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
 	vcpu->arch.timing_exit.tv64 = 0;
 	vcpu->arch.timing_last_enter.tv64 = 0;
 
-	mutex_unlock(&vcpu->mutex);
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
 }
 
 static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
@@ -65,6 +65,8 @@  static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
 		return;
 	}
 
+	mutex_lock(&vcpu->arch.exit_timing_lock);
+
 	vcpu->arch.timing_count_type[type]++;
 
 	/* sum */
@@ -93,6 +95,8 @@  static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
 		vcpu->arch.timing_min_duration[type] = duration;
 	if (unlikely(duration > vcpu->arch.timing_max_duration[type]))
 		vcpu->arch.timing_max_duration[type] = duration;
+
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
 }
 
 void kvmppc_update_timing_stats(struct kvm_vcpu *vcpu)