[PATCH 3/4] KVM: Fix spinlock taken warning during host resume

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpengli@tencent.com>

 WARNING: CPU: 0 PID: 13554 at kvm/arch/x86/kvm//../../../virt/kvm/kvm_main.c:4183 kvm_resume+0x3c/0x40 [kvm]
  CPU: 0 PID: 13554 Comm: step_after_susp Tainted: G           OE     5.1.0-rc4+ #1
  RIP: 0010:kvm_resume+0x3c/0x40 [kvm]
  Call Trace:
   syscore_resume+0x63/0x2d0
   suspend_devices_and_enter+0x9d1/0xa40
   pm_suspend+0x33a/0x3b0
   state_store+0x82/0xf0
   kobj_attr_store+0x12/0x20
   sysfs_kf_write+0x4b/0x60
   kernfs_fop_write+0x120/0x1a0
   __vfs_write+0x1b/0x40
   vfs_write+0xcd/0x1d0
   ksys_write+0x5f/0xe0
   __x64_sys_write+0x1a/0x20
   do_syscall_64+0x6f/0x6c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Commit ca84d1a24 (KVM: x86: Add clock sync request to hardware enable) mentioned 
that "we always hold kvm_lock when hardware_enable is called.  The one place that 
doesn't need to worry about it is resume, as resuming a frozen CPU, the spinlock 
won't be taken." However, commit 6706dae9 (virt/kvm: Replace spin_is_locked() with 
lockdep) introduces a bug, it asserts when the lock is not held which is contrary 
to the original goal. 

This patch fixes it by WARN_ON when the lock is held.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5fb0f16..c7eab5f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4096,7 +4096,7 @@ static int kvm_suspend(void)
 static void kvm_resume(void)
 {
 	if (kvm_usage_count) {
-		lockdep_assert_held(&kvm_count_lock);
+		WARN_ON(lockdep_is_held(&kvm_count_lock));
 		hardware_enable_nolock(NULL);
 	}
 }
-- 
2.7.4