linux-kernel - Re: [PATCH AUTOSEL 5.4 02/11] KVM: Fix lockdep false negative during host resume

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Message-ID: <3fee5315-e55d-278c-e522-d0e6fb2cadd0@redhat.com>
Date:   Tue, 1 Mar 2022 21:22:18 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>, kvm@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.4 02/11] KVM: Fix lockdep false negative during
 host resume

On 3/1/22 21:19, Sasha Levin wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> [ Upstream commit 4cb9a998b1ce25fad74a82f5a5c45a4ef40de337 ]
> 
> I saw the below splatting after the host suspended and resumed.
> 
>     WARNING: CPU: 0 PID: 2943 at kvm/arch/x86/kvm/../../../virt/kvm/kvm_main.c:5531 kvm_resume+0x2c/0x30 [kvm]
>     CPU: 0 PID: 2943 Comm: step_after_susp Tainted: G        W IOE     5.17.0-rc3+ #4
>     RIP: 0010:kvm_resume+0x2c/0x30 [kvm]
>     Call Trace:
>      <TASK>
>      syscore_resume+0x90/0x340
>      suspend_devices_and_enter+0xaee/0xe90
>      pm_suspend.cold+0x36b/0x3c2
>      state_store+0x82/0xf0
>      kernfs_fop_write_iter+0x1b6/0x260
>      new_sync_write+0x258/0x370
>      vfs_write+0x33f/0x510
>      ksys_write+0xc9/0x160
>      do_syscall_64+0x3b/0xc0
>      entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> lockdep_is_held() can return -1 when lockdep is disabled which triggers
> this warning. Let's use lockdep_assert_not_held() which can detect
> incorrect calls while holding a lock and it also avoids false negatives
> when lockdep is disabled.
> 
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> Message-Id: <1644920142-81249-1-git-send-email-wanpengli@...cent.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   virt/kvm/kvm_main.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index f31976010622f..adda0c6672b56 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4427,9 +4427,7 @@ static int kvm_suspend(void)
>   static void kvm_resume(void)
>   {
>   	if (kvm_usage_count) {
> -#ifdef CONFIG_LOCKDEP
> -		WARN_ON(lockdep_is_held(&kvm_count_lock));
> -#endif
> +		lockdep_assert_not_held(&kvm_count_lock);
>   		hardware_enable_nolock(NULL);
>   	}
>   }

Acked-by: Paolo Bonzini <pbonzini@...hat.com>