On 07/06/2017 14:04, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) > adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs > when needed, to protect the code that needs use rcu. There is no need to call > this pairs if async page fault is not triggered from idle task. > > This patch fixes it by rcu irq exit if it is not triggered from idle task to > avoid rcu hang after schedule() in the for loop. How does the bug manifest? Paolo > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > --- > arch/x86/kernel/kvm.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 43e10d6..e70ed72 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -141,6 +141,8 @@ void kvm_async_pf_task_wait(u32 token) > n.token = token; > n.cpu = smp_processor_id(); > n.halted = is_idle_task(current) || preempt_count() > 1; > + if (!n.halted) > + rcu_irq_exit(); > init_swait_queue_head(&n.wq); > hlist_add_head(&n.link, &b->list); > raw_spin_unlock(&b->lock); > @@ -167,8 +169,9 @@ void kvm_async_pf_task_wait(u32 token) > } > if (!n.halted) > finish_swait(&n.wq, &wait); > + else > + rcu_irq_exit(); > > - rcu_irq_exit(); > return; > }
