linux-kernel - Re: [PATCH v3 10/16] iommu: introduce device fault report API

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Date:   Fri, 8 Dec 2017 13:22:48 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Lan Tianyu <tianyu.lan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Jean Delvare <khali@...ux-fr.org>,
        "Christoph Hellwig" <hch@...radead.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 10/16] iommu: introduce device fault report API

On Fri, 8 Dec 2017 13:59:09 -0700
Alex Williamson <alex.williamson@...hat.com> wrote:

> > > 
> > > Isn't this all rather racy?  I see that we can have multiple
> > > callers to register racing.    
> > I agree, should use a lock here to prevent unregister. For multiple
> > caller race, it won't happen since there is only one caller can
> > register handler.  
> 
> If you have multiple simultaneous callers to
> iommu_register_device_fault_handler, they can all get past the test
> for fault_param (testing and setting is not atomic), then it's
> indeterminate which handler gets installed.  Thanks,
> 
I see, having the mutex would prevent it. Later callers would get
-EBUSY.
Thanks a lot!
> Alex