linux-kernel - Re: [PATCH 4/8] x86/platform/uv: Setup UV functions for Hubless UV Systems

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Message-ID: <e10cd5c2-c0b0-60f6-ee49-12ff62a483ef@hpe.com>
Date:   Wed, 11 Sep 2019 13:58:45 -0700
From:   Mike Travis <mike.travis@....com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@...radead.org>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Hedi Berriche <hedi.berriche@....com>,
        Steve Wahl <steve.wahl@....com>,
        Justin Ernst <justin.ernst@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] x86/platform/uv: Setup UV functions for Hubless UV
 Systems



On 9/11/2019 1:44 PM, Mike Travis wrote:
> 
> 
> On 9/10/2019 11:07 PM, Ingo Molnar wrote:
>>
>> * Mike Travis <mike.travis@....com> wrote:
>>
>>> +/* Initialize UV hubless systems */
>>> +static __init int uv_system_init_hubless(void)
>>> +{
>>> +    int rc;
>>> +
>>> +    /* Setup PCH NMI handler */
>>> +    uv_nmi_setup_hubless();
>>> +
>>> +    /* Init kernel/BIOS interface */
>>> +    rc = uv_bios_init();
>>> +
>>> +    return rc;
>>> +}
> 
> This looks like an excessive cleanup error by me.  The original was:
> 
>> +static __init int uv_system_init_hubless(void)
>> +{
>> +       int rc;
>> +
>> +       /* Setup PCH NMI handler */
>> +       uv_nmi_setup_hubless();
>> +
>> +       /* Init kernel/BIOS interface */
>> +       rc = uv_bios_init();
>> +
>> +       /* Create user access node if UVsystab available */
>> +       if (rc >= 0)
>> +               uv_setup_proc_files(1);
>> +
>> +       return rc;
>> +}
>> +
> 
> Hubbed UV's do not have a non-UV BIOS, but hubless systems in theory 
> can.   So uv_bios_init can fail on hubless systems if it has some other 
> BIOS (unlikely but possible).  So I removed too much in this cleanup. 
> I'll send another patch set that puts this back.

I discovered the problem... In a rearrangement of the patches this 
change does happen but in a later patch [5/8]:

  /* Initialize UV hubless systems */
  static __init int uv_system_init_hubless(void)
  {
@@ -1468,6 +1555,10 @@ static __init int uv_system_init_hubless
         /* Init kernel/BIOS interface */
         rc = uv_bios_init();

+       /* Create user access node if UVsystab available */
+       if (rc >= 0)
+               uv_setup_proc_files(1);
+
         return rc;
  }

The mistake you saw [in patch 3/8] is very short lived... Hopefully no 
need for another patch set?

> 
> Thanks,
> Mike
> 
>>
>> Am I the only one who immediately sees the trivial C transformation
>> through which this function could lose a local variable and become 4
>> lines shorter?
>>
>> And this function got two Reviewed-by tags...
>>
>> Thanks,
>>
>>     Ingo
>>