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. 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; } EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait); -- 2.7.4
