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SubjectRe: [PATCH 3/4] KVM: Fix spinlock taken warning during host resume
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On 17/05/19 10:49, Wanpeng Li wrote:
> 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);
> }
> }
>

Queued, thanks.

Paolo

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