linux-kernel - Re: [PATCH v2 1/2] iommu: Use mutex instead of spinlock for iommu_device

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Date: Mon, 29 Jan 2024 10:57:31 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] iommu: Use mutex instead of spinlock for
 iommu_device_list

On Mon, Jan 29, 2024 at 08:04:35AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > Sent: Friday, January 26, 2024 6:54 PM
> > 
> > The iommu_device_lock spinlock was used to protect the iommu device
> > list. However, there is no requirement to access the iommu device
> > list in interrupt context. Therefore, a mutex is sufficient.
> 
> I don't think that interrupt is the reason for spinlock otherwise
> spin_lock_irqsave() should be used instead.

Right, there is no touch of this from an interrupt

I suspect it is following the the general kernel wisdom that a
spinlock is better if the critical sections are very small.

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason