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@xxxxxxxxxxxxx>
---
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
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