linux-kernel - Re: [PATCH 3/5] iommu/s390: Use RCU to allow concurrent domain

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Message-ID: <Y07Dz/NROAMI0Hku@nvidia.com>
Date:   Tue, 18 Oct 2022 12:18:39 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Matthew Rosato <mjrosato@...ux.ibm.com>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] iommu/s390: Use RCU to allow concurrent domain_list
 iteration

On Tue, Oct 18, 2022 at 04:51:30PM +0200, Niklas Schnelle wrote:

> @@ -84,7 +88,7 @@ static void __s390_iommu_detach_device(struct zpci_dev *zdev)
>  		return;
>  
>  	spin_lock_irqsave(&s390_domain->list_lock, flags);
> -	list_del_init(&zdev->iommu_list);
> +	list_del_rcu(&zdev->iommu_list);
>  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);

This doesn't seem obviously OK, the next steps remove the translation
while we can still have concurrent RCU protected flushes going on.

Is it OK to call the flushes when after the zpci_dma_exit_device()/etc?

Jason