linux-kernel - Re: [PATCH] x86: Fix RCU list usage to avoid false positive warnings

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Message-ID: <6c992b7f-c6c7-44a6-fa5a-c3512646de05@redhat.com>
Date:   Mon, 4 May 2020 18:47:43 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     madhuparnabhowmik10@...il.com, mingo@...hat.com, bp@...en8.de
Cc:     x86@...nel.org, bhelgaas@...gle.com,
        sean.j.christopherson@...el.com, cai@....pw, paulmck@...nel.org,
        joel@...lfernandes.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        frextrite@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] x86: Fix RCU list usage to avoid false positive warnings

On 30/04/20 21:29, madhuparnabhowmik10@...il.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> 
> Use list_for_each_entry() instead of list_for_each_entry_rcu() whenever
> spinlock or mutex is always held.
> Otherwise, pass cond to list_for_each_entry_rcu().
> 
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> ---
>  arch/x86/kernel/nmi.c          | 2 +-
>  arch/x86/kvm/irq_comm.c        | 3 ++-
>  arch/x86/pci/mmconfig-shared.c | 2 +-
>  3 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
> index 6407ea21fa1b..999dc6c134d2 100644
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -195,7 +195,7 @@ void unregister_nmi_handler(unsigned int type, const char *name)
>  
>  	raw_spin_lock_irqsave(&desc->lock, flags);
>  
> -	list_for_each_entry_rcu(n, &desc->head, list) {
> +	list_for_each_entry(n, &desc->head, list) {
>  		/*
>  		 * the name passed in to describe the nmi handler
>  		 * is used as the lookup key
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index c47d2acec529..5b88a648e079 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -258,7 +258,8 @@ void kvm_fire_mask_notifiers(struct kvm *kvm, unsigned irqchip, unsigned pin,
>  	idx = srcu_read_lock(&kvm->irq_srcu);
>  	gsi = kvm_irq_map_chip_pin(kvm, irqchip, pin);
>  	if (gsi != -1)
> -		hlist_for_each_entry_rcu(kimn, &kvm->arch.mask_notifier_list, link)
> +		hlist_for_each_entry_rcu(kimn, &kvm->arch.mask_notifier_list, link,
> +					srcu_read_lock_held(&kvm->irq_srcu))
>  			if (kimn->irq == gsi)
>  				kimn->func(kimn, mask);
>  	srcu_read_unlock(&kvm->irq_srcu, idx);
> diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
> index 6fa42e9c4e6f..a096942690bd 100644
> --- a/arch/x86/pci/mmconfig-shared.c
> +++ b/arch/x86/pci/mmconfig-shared.c
> @@ -797,7 +797,7 @@ int pci_mmconfig_delete(u16 seg, u8 start, u8 end)
>  	struct pci_mmcfg_region *cfg;
>  
>  	mutex_lock(&pci_mmcfg_lock);
> -	list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list)
> +	list_for_each_entry(cfg, &pci_mmcfg_list, list)
>  		if (cfg->segment == seg && cfg->start_bus == start &&
>  		    cfg->end_bus == end) {
>  			list_del_rcu(&cfg->list);
> 

For KVM parts, if the x86 maintainers want to apply the whole patch,

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

Paolo