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Subject: Re: [PATCH 3/4] KVM: Fix spinlock taken warning during host resume
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        "Paul E . McKenney" <paulmck@linux.ibm.com>
References: <1558082990-7822-1-git-send-email-wanpengli@tencent.com>
 <1558082990-7822-3-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <7cce6762-006a-a21c-6400-6c0166428cf1@redhat.com>
Date:   Mon, 20 May 2019 12:36:30 +0200
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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