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

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Message-ID: <7c4383ac-0b0b-dd43-9958-dbd4abeea63f@linux.intel.com>
Date:   Wed, 7 Sep 2022 17:33:03 +0800
From:   Ethan Zhao <haifeng.zhao@...ux.intel.com>
To:     John Garry <john.garry@...wei.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

John,

在 2022/9/6 18:50, John Garry 写道:
> On 06/09/2022 10:28, Ethan Zhao wrote:
>
> Hi Ethan,
>
>>> Signed-off-by: John Garry <john.garry@...wei.com>
>>> Reviewed-by: Robin Murphy <robin.murphy@....com>
>>> ---
>>>   drivers/iommu/iova.c | 7 ++-----
>>>   1 file changed, 2 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
>>> index 47d1983dfa2a..580fdf669922 100644
>>> --- a/drivers/iommu/iova.c
>>> +++ b/drivers/iommu/iova.c
>>> @@ -661,9 +661,6 @@ iova_magazine_free_pfns(struct iova_magazine 
>>> *mag, struct iova_domain *iovad)
>>>       unsigned long flags;
>>>       int i;
>>> -    if (!mag)
>>> -        return;
>>> -
>>
>> iommu_probe_device
>>    ops->probe_finalize(dev);
>>      intel_iommu_probe_finalize
>>         iommu_setup_dma_ops
>>           iommu_dma_init_domain(domain, dma_base, dma_limit, dev)
>>             iova_domain_init_rcaches
>>               {
>>               ...
>>               cpu_rcache->loaded = iova_magazine_alloc(GFP_KERNEL);
>>               cpu_rcache->prev = iova_magazine_alloc(GFP_KERNEL);
>>             if (!cpu_rcache->loaded || !cpu_rcache->prev) {
>>                  ret = -ENOMEM;
>>                        goto out_err;
>>
>> 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.


Thanks,

Ethan

>
> However we have a !iovad->rcache check on the "fast" alloc but not 
> "insert". I need to check why that is again.
>
> Thanks,
> john

-- 
"firm, enduring, strong, and long-lived"