linux-kernel - Re: [patch V2 02/31] genirq/msi: Add mutex for MSI list protection

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Message-ID: <87bl1pzgnd.ffs@tglx>
Date:   Thu, 09 Dec 2021 21:07:18 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Megha Dey <megha.dey@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-pci@...r.kernel.org,
        Cedric Le Goater <clg@...d.org>,
        xen-devel@...ts.xenproject.org, Juergen Gross <jgross@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <allenbh@...il.com>, linux-ntb@...glegroups.com
Subject: Re: [patch V2 02/31] genirq/msi: Add mutex for MSI list protection

On Wed, Dec 08 2021 at 20:47, Jason Gunthorpe wrote:
> On Mon, Dec 06, 2021 at 11:51:05PM +0100, Thomas Gleixner wrote:
>> +++ b/kernel/irq/msi.c
>> @@ -127,12 +127,37 @@ int msi_setup_device_data(struct device
>>  		return -ENOMEM;
>>  
>>  	INIT_LIST_HEAD(&md->list);
>> +	mutex_init(&md->mutex);
>>  	dev->msi.data = md;
>>  	devres_add(dev, md);
>>  	return 0;
>>  }
>>  
>>  /**
>> + * msi_lock_descs - Lock the MSI descriptor storage of a device
>> + * @dev:	Device to operate on
>> + */
>> +void msi_lock_descs(struct device *dev)
>> +{
>> +	if (WARN_ON_ONCE(!dev->msi.data))
>> +		return;
>
> Is this useful? Other places that call msi_lock_descs will continue on and deref
> null dev->msi anyhow - is the dump from the WARN_ON that much better
> than the oops from the null deref here:
>
>> +	mutex_lock(&dev->msi.data->mutex);

I put it there for paranoia reasons and forgot to revist it later. In
that case yes, it's of questionable value.

Thanks,

        tglx