linux-kernel - Re: [PATCH 01/16] x86/PCI: Replace spin_is

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Message-ID: <20181003160051.GF120535@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 3 Oct 2018 11:00:51 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lance Roy <ldr709@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH 01/16] x86/PCI: Replace spin_is_locked() with lockdep

On Tue, Oct 02, 2018 at 10:38:47PM -0700, Lance Roy wrote:
> lockdep_assert_held() is better suited to checking locking requirements,
> since it won't get confused when someone else holds the lock. This is
> also a step towards possibly removing spin_is_locked().
> 
> Signed-off-by: Lance Roy <ldr709@...il.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: <x86@...nel.org>
> Cc: <linux-pci@...r.kernel.org>

I assume you plan to merge the whole series together.  I don't object
to that, but I don't know enough to be able to formally ack this.

It would be useful to include a tiny bit more detail in the changelog.
The spin_is_locked() documentation doesn't mention anything about
differences with respect to the lock being held by self vs by someone
else, so I can't tell where the confusion arises.

Bjorn

> ---
>  arch/x86/pci/i386.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
> index ed4ac215305d..24bb58a007de 100644
> --- a/arch/x86/pci/i386.c
> +++ b/arch/x86/pci/i386.c
> @@ -59,7 +59,7 @@ static struct pcibios_fwaddrmap *pcibios_fwaddrmap_lookup(struct pci_dev *dev)
>  {
>  	struct pcibios_fwaddrmap *map;
>  
> -	WARN_ON_SMP(!spin_is_locked(&pcibios_fwaddrmap_lock));
> +	lockdep_assert_held(&pcibios_fwaddrmap_lock);
>  
>  	list_for_each_entry(map, &pcibios_fwaddrmappings, list)
>  		if (map->dev == dev)
> -- 
> 2.19.0
>