linux-kernel - Re: [PATCH v2 1/2] iova: Remove some magazine pointer NULL checks

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Date:   Wed, 7 Sep 2022 10:53:39 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ethan Zhao <haifeng.zhao@...ux.intel.com>, <robin.murphy@....com>,
        <joro@...tes.org>, <will@...nel.org>
CC:     <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...wei.com>
Subject: Re: [PATCH v2 1/2] iova: Remove some magazine pointer NULL checks

On 07/09/2022 10:33, Ethan Zhao wrote:

Hi Ethan,

>>> Do you mean iova_magazine_alloc() is impossible to fail ?
>>
>> No, iova_magazine_alloc() may fail and return NULL. But if it does 
>> then we set iovad rcache pointer = NULL in the error path and don't 
>> use the rcache.
> 
> Yup,  if iova_magazine_alloc() failed ,
> 
> iovad->rcaches = NULL;
> 
> was set by free_iova_rcaches()
> 
> in error path of iova_domain_init_rcache().
> 
> and checked in
> 
> alloc_iova_fast()->iova_rcache_get().
> 
> More comment in code would wipe off my curiosity.

As discussed with Robin, we will actually remove that check in 
iova_rcache_get() for now and in future make the IOVA domain init more 
robust.

As for the "loaded" and "prev" NULL checks removal in this specific 
patch, I will add more words in the commit message to make it clearer 
that failure in init was the only way in which they NULL previously.

thanks,
John