Re: [v1][PATCH 1/1] KVM: PPC: disable preemption when using hard_irq_disable()

["tiejun.chen" <tiejun.chen@windriver.com>]

On 07/10/2013 05:49 PM, Alexander Graf wrote:
>
> On 10.07.2013, at 08:02, Tiejun Chen wrote:
>
>> We should ensure the preemption cannot occur while calling get_paca()
>> insdide hard_irq_disable(), otherwise the paca_struct may be the
>> wrong one just after. And btw, we may update timing stats in this case.
>>
>> Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
>> ---
>> arch/powerpc/kvm/booke.c |    2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
>> index dcc94f0..9dae25d 100644
>> --- a/arch/powerpc/kvm/booke.c
>> +++ b/arch/powerpc/kvm/booke.c
>> @@ -839,6 +839,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
>> 	WARN_ON(local_paca->irq_happened != 0);
>> #endif
>>
>> +	preempt_disable();
>> 	/*
>> 	 * We enter with interrupts disabled in hardware, but
>> 	 * we need to call hard_irq_disable anyway to ensure that
>> @@ -848,6 +849,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
>>
>> 	/* update before a new last_exit_type is rewritten */
>> 	kvmppc_update_timing_stats(vcpu);
>> +	preempt_enable();
>
> All of the code here is already called with interrupts disabled. I don't see how we could preempt then?

But the kernel still check this in preempt case,

#define get_paca()      ((void) debug_smp_processor_id(), local_paca)

then trigger that known call trace as I observed :)

BUG: using smp_processor_id() in preemptible [00000000] code: qemu-system-ppc/2065
caller is .kvmppc_handle_exit+0x48/0x810
CPU: 0 PID: 2065 Comm: qemu-system-ppc Not tainted 3.10.0-172036-ge2daa28-dirty #116
Call Trace:
[c0000001fc637570] [c00000000000835c] .show_stack+0x7c/0x1f0 (unreliable)
[c0000001fc637640] [c000000000673a0c] .dump_stack+0x28/0x3c
[c0000001fc6376b0] [c0000000002f04d8] .debug_smp_processor_id+0x108/0x120
[c0000001fc637740] [c0000000000444e8] .kvmppc_handle_exit+0x48/0x810
[c0000001fc6377f0] [c000000000047c80] .kvmppc_resume_host+0xa4/0xf8

Tiejun