linux-kernel - Re: [PATCH] iommu/amd: fix missing tag from dev

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Date:   Tue, 3 Jul 2018 17:24:12 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     "Hook, Gary" <ghook@....com>, Joe Perches <joe@...ches.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: fix missing tag from dev_err message

On 03/07/18 17:21, Hook, Gary wrote:
> On 7/3/2018 10:55 AM, Joe Perches wrote:
>> On Tue, 2018-07-03 at 07:56 -0500, Gary R Hook wrote:
>>> On 07/03/2018 05:07 AM, Joe Perches wrote:
>>>> On Tue, 2018-07-03 at 07:40 +0100, Colin King wrote:
>>>>> Currently tag is being assigned but not used, it is missing from
>>>>> the dev_err message, so add it in.
>>>>>
>>>>> Cleans up clang warning:
>>>>> warning: variable 'tag' set but not used [-Wunused-but-set-variable]
>>>>
>>>> []
>>>>> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
>>>>
>>>> []
>>>>> @@ -616,9 +616,9 @@ static void iommu_print_event(struct amd_iommu
>>>>> *iommu, void *__evt)
>>>>>            pasid = ((event[0] >> 16) & 0xFFFF)
>>>>>                | ((event[1] << 6) & 0xF0000);
>>>>>            tag = event[1] & 0x03FF;
>>>>> -        dev_err(dev, "INVALID_PPR_REQUEST device=%02x:%02x.%x
>>>>> pasid=0x%05x address=0x%016llx flags=0x%04x]\n",
>>>>> +        dev_err(dev, "INVALID_PPR_REQUEST device=%02x:%02x.%x
>>>>> pasid=0x%05x address=0x%016llx flags=0x%04x tag=0x%03x]\n",
>>>>>                PCI_BUS_NUM(devid), PCI_SLOT(devid), PCI_FUNC(devid),
>>>>> -            pasid, address, flags);
>>>>> +            pasid, address, flags, tag);
>>>>
>>>> Seems to have a superfluous ] that should be removed.
>>>
>>> Yeah, I pretty much messed up all of the log messages in that function.
>>> My apologies. I'll create a patch for that problem; it shouldn't be
>>> fixed here.
> 
> Well, no, I misremembered. The extraneous square brace has been there
> forever. Needs fixin', though.
> 

The opening square bracket is much earlier:

dev_err(dev, "AMD-Vi: Event logged [");

..and all the subsequent dev_err messages have the trailing square bracket.



> 
>> I also wonder why event is declared volatile and then
>> dereferenced with [<constant>] multiple times.
>>
>> Maybe each array dereference should be stored as a
>> local variable instead.
> 
> (I know you know this, but as I understand it) Event is pointing into
> the (hardware's) event buffer, and the data structure has the potential
> of changing out from under us if the device does something without our
> knowledge. Since volatile hints to the compiler of this possibility, I
> believe the compiler should manage this situation. But I could be wrong.
> 
> I don't know that we need to atomically copy all 16 bytes into a local
> buffer, as I don't think it's possible for the device to step on itself.
> It will just stop recording events if the buffer gets full. At this
> moment I think volatile is overkill, at least for the EPYC/Ryzen IOMMU.