linux-kernel - Re: [PATCH] mce-apei: do not rely on ACPI_ERST_GET_RECORD

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Date:	Thu, 3 Mar 2016 16:53:16 -0500
From:	Josef Bacik <jbacik@...com>
To:	"Luck, Tony" <tony.luck@...el.com>
CC:	<bp@...en8.de>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<hpa@...or.com>, <x86@...nel.org>, <linux-edac@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mce-apei: do not rely on ACPI_ERST_GET_RECORD_ID for
 record id

On 03/03/2016 04:49 PM, Luck, Tony wrote:
>>   retry:
>> -	rc = erst_get_record_id_next(&pos, record_id);
>> -	if (rc)
>> -		goto out;
>> +	/*
>> +	 * Some hardware is broken and doesn't actually advance the record id
>
> I'd blame this on firmware rather than hardware.

Yup sorry misspoke.

>
>> +	 * returned by ACPI_ERST_GET_RECORD_ID when we read a record like the
>> +	 * spec says it is supposed to.  So instead use record_id == 0 to just
>> +	 * grab the first record in the erst, and fall back only if we trip over
>> +	 * a record that isn't a MCE record.
>> +	 */
>> +	if (lookup_record) {
>> +		rc = erst_get_record_id_next(&pos, record_id);
>> +		if (rc)
>> +			goto out;
>> +	} else {
>> +		*record_id = 0;
>> +	}
>>   	/* no more record */
>>   	if (*record_id == APEI_ERST_INVALID_RECORD_ID)
>>   		goto out;
>>   	rc = erst_read(*record_id, &rcd.hdr, sizeof(rcd));
>> -	/* someone else has cleared the record, try next one */
>> -	if (rc == -ENOENT)
>> -		goto retry;
>> -	else if (rc < 0)
>> +	/*
>> +	 * someone else has cleared the record, try next one if we are looking
>> +	 * up records.  If we aren't looking up the record id's then just bail
>> +	 * since this means we have an empty table.
>> +	 */
>> +	if (rc == -ENOENT) {
>> +		if (lookup_record)
>> +			goto retry;
>> +		rc = 0;
>> +		goto out;
>> +	} else if (rc < 0) {
>>   		goto out;
>> -	/* try to skip other type records in storage */
>> -	else if (rc != sizeof(rcd) ||
>> -		 uuid_le_cmp(rcd.hdr.creator_id, CPER_CREATOR_MCE))
>> +	} else if (rc != sizeof(rcd) ||
>> +		 uuid_le_cmp(rcd.hdr.creator_id, CPER_CREATOR_MCE)) {
>> +		/* try to skip other type records in storage */
>> +		lookup_record = true;
>>   		goto retry;
>
> Are you still doomed by the buggy firmware if we take this "goto"?
> You be back at the top of the loop excpecting erst_get_record_id_next()
> to move on.  Does this just not happen in practice (finding non MCE
> records in amognst the MCE ones)?
>

So one of the boxes had a non MCE record with MCE records, but yeah it 
was on a box that was also broken in this way.  I'm not super worried 
about this case for us, I just want to have a fallback for any firmware 
that may not be broken in this way to be able to skip things.  Thanks,

Josef