Re: [kvm:queue 41/42] arch/s390/kvm/interrupt.c:428:12: warning: ignoring return value of 'vcpu_load', declared with attribute warn_unused_result

[Michael S. Tsirkin]

On Thu, Sep 20, 2012 at 08:16:08AM +0800, Fengguang Wu wrote:
> Hi Michael,
> 
> FYI, there are new compile warnings show up in
> 
> tree:   git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
> head:   879238fecc051d95037ae76332916209a7770709
> commit: 9fc77441e5e1bf80b794cc546d2243ee9f4afb75 [41/42] KVM: make processes 
> waiting on vcpu mutex killable
> config: s390-defconfig
> 
> All error/warnings:
> 
> arch/s390/kvm/interrupt.c: In function 'kvm_s390_handle_wait':
> arch/s390/kvm/interrupt.c:428:12: warning: ignoring return value of 
> 'vcpu_load', declared with attribute warn_unused_result [-Wunused-result]
> 
> vim +428 arch/s390/kvm/interrupt.c
>    418                add_wait_queue(&vcpu->arch.local_int.wq, &wait);
>    419                while (list_empty(&vcpu->arch.local_int.list) &&
>    420                        
> list_empty(&vcpu->arch.local_int.float_int->list) &&
>    421                        (!vcpu->arch.local_int.timer_due) &&
>    422                        !signal_pending(current)) {
>    423                        set_current_state(TASK_INTERRUPTIBLE);
>    424                        spin_unlock_bh(&vcpu->arch.local_int.lock);
>    425                        
> spin_unlock(&vcpu->arch.local_int.float_int->lock);
>    426                        vcpu_put(vcpu);
>    427                        schedule();
>  > 428                        vcpu_load(vcpu);
>    429                        
> spin_lock(&vcpu->arch.local_int.float_int->lock);
>    430                        spin_lock_bh(&vcpu->arch.local_int.lock);
>    431                }
>    432                __unset_cpu_idle(vcpu);
>    433                __set_current_state(TASK_RUNNING);
>    434                remove_wait_queue(&vcpu->arch.local_int.wq, &wait);
>    435                spin_unlock_bh(&vcpu->arch.local_int.lock);
>    436                spin_unlock(&vcpu->arch.local_int.float_int->lock);
>    437                hrtimer_try_to_cancel(&vcpu->arch.ckc_timer);
>    438                return 0;


Thanks for the report.  This is because vcpu_load can now fail if task
is being killed.  I'm guessing the following is the right fix but have
no way to tell. Warning: completely untested.

--->

kvm/arm: handle vcpu_load failure gracefully

Signed-off-by: Michael S. Tsirkin <m...@redhat.com>

-- 

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index b7bc1aa..5aedf25 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -362,6 +362,7 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
 {
        u64 now, sltime;
        DECLARE_WAITQUEUE(wait, current);
+       int ret;
 
        vcpu->stat.exit_wait_state++;
        if (kvm_cpu_has_interrupt(vcpu))
@@ -407,7 +408,9 @@ no_timer:
                spin_unlock(&vcpu->arch.local_int.float_int->lock);
                vcpu_put(vcpu);
                schedule();
-               vcpu_load(vcpu);
+               ret = vcpu_load(vcpu);
+               if (ret)
+                       goto cancel;
                spin_lock(&vcpu->arch.local_int.float_int->lock);
                spin_lock_bh(&vcpu->arch.local_int.lock);
        }
@@ -416,6 +419,7 @@ no_timer:
        remove_wait_queue(&vcpu->arch.local_int.wq, &wait);
        spin_unlock_bh(&vcpu->arch.local_int.lock);
        spin_unlock(&vcpu->arch.local_int.float_int->lock);
+cancel:
        hrtimer_try_to_cancel(&vcpu->arch.ckc_timer);
        return 0;
 }

> ---
> 0-DAY kernel build testing backend         Open Source Technology Centre
> Fengguang Wu, Yuanhan Liu                              Intel Corporation
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