linux-kernel - Re: [PATCH v3 3/5] acpi, apei, ghes: Introduce more generic mechanism to init/deinit GHES error notifications.

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Date:	Tue, 24 Jun 2014 11:06:28 +0200
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Robert Richter <rric@...nel.org>
CC:	rjw@...ysocki.net, lenb@...nel.org, tony.luck@...el.com,
	bp@...en8.de, m.chehab@...sung.com, bp@...e.de,
	linux-edac@...r.kernel.org, x86@...nel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linaro-acpi@...ts.linaro.org
Subject: Re: [PATCH v3 3/5] acpi, apei, ghes: Introduce more generic mechanism
 to init/deinit GHES error notifications.

On 13.06.2014 15:10, Robert Richter wrote:
> On 13.06.14 13:02:58, Tomasz Nowicki wrote:
>
>> @@ -811,6 +819,8 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
>>   	int sev, sev_global = -1;
>>   	int ret = NMI_DONE;
>>
>> +	BUG_ON(!IS_ENABLED(ARCH_HAS_ACPI_APEI_NMI));
>> +
>
> Now that we have the ARCH_HAS_ACPI_APEI_NMI option, group nmi code,
> put it in an #ifdef ... and make function stubs for the !nmi case
> where necessary. That code should moved to patch #2. If an arch does
> not support nmi code, we don't want to compile it into the kernel.
>
> Also this patch is quit a bit large and should further split into
> moving functional code into separate functions and the introduction of
> the notifier setup. This makes review much easier.
>
> I did not yet took a deep look into your notifier framework, but I
> don't really see a reason for the dynamic collection of function
> pointers in ghes_notify_tab. See below.
>
>>   	raw_spin_lock(&ghes_nmi_lock);
>>   	list_for_each_entry_rcu(ghes, &ghes_nmi, list) {
>>   		if (ghes_read_estatus(ghes, 1)) {
>> @@ -875,10 +885,6 @@ out:
>>   	return ret;
>>   }
>
>> +static int ghes_notify_init_nmi(struct ghes *ghes)
>> +{
>> +	unsigned long len;
>> +	int status = 0;
>> +
>> +	len = ghes_esource_prealloc_size(ghes->generic);
>> +	ghes_estatus_pool_expand(len);
>> +	mutex_lock(&ghes_list_mutex);
>> +	if (list_empty(&ghes_nmi))
>> +		status = register_nmi_handler(NMI_LOCAL, ghes_notify_nmi, 0,
>> +					      "ghes");
>> +	list_add_rcu(&ghes->list, &ghes_nmi);
>> +	mutex_unlock(&ghes_list_mutex);
>> +
>> +	return status;
>> +}
>> +
>> +static void ghes_notify_remove_nmi(struct ghes *ghes)
>> +{
>> +	unsigned long len;
>> +
>> +	mutex_lock(&ghes_list_mutex);
>> +	list_del_rcu(&ghes->list);
>> +	if (list_empty(&ghes_nmi))
>> +		unregister_nmi_handler(NMI_LOCAL, "ghes");
>> +	mutex_unlock(&ghes_list_mutex);
>> +	/*
>> +	 * To synchronize with NMI handler, ghes can only be
>> +	 * freed after NMI handler finishes.
>> +	 */
>> +	synchronize_rcu();
>> +	len = ghes_esource_prealloc_size(ghes->generic);
>> +	ghes_estatus_pool_shrink(len);
>> +}
>> +
>> +static void ghes_init_nmi(void)
>> +{
>> +	if (!IS_ENABLED(ARCH_HAS_ACPI_APEI_NMI))
>> +		return;
>> +
>> +	init_irq_work(&ghes_proc_irq_work, ghes_proc_in_irq);
>> +	ghes_notify_tab[ACPI_HEST_NOTIFY_NMI].init_call = ghes_notify_init_nmi;
>> +	ghes_notify_tab[ACPI_HEST_NOTIFY_NMI].remove_call =
>> +							ghes_notify_remove_nmi;
>> +}
>> +
>
> So this is the only code of your whole patch set that actually changes
> an entry, and just one time only during nmi init. Thus, there is no
> need at all for ghes_notify_tab. Just create function stubs for
> ghes_notify_{init,remove}_nmi for the !nmi case with the error message
> in it and call the functions directly in the switch/cases.
>
>> +static struct ghes_notify_setup
>> +	ghes_notify_tab[ACPI_HEST_NOTIFY_RESERVED] = {
>> +		[ACPI_HEST_NOTIFY_POLLED]   = {"POLLED",
>> +					       ghes_notify_init_polled,
>> +					       ghes_notify_remove_polled},
>> +		[ACPI_HEST_NOTIFY_EXTERNAL] = {"EXT_IRQ",
>> +					       ghes_notify_init_external,
>> +					       ghes_notify_remove_external},
>> +		[ACPI_HEST_NOTIFY_LOCAL]    = {"LOCAL_IRQ", NULL, NULL},
>> +		[ACPI_HEST_NOTIFY_SCI]      = {"SCI",
>> +					       ghes_notify_init_sci,
>> +					       ghes_notify_remove_sci},
>> +		[ACPI_HEST_NOTIFY_NMI]      = {"NMI", NULL, NULL},
>> +		[ACPI_HEST_NOTIFY_CMCI]     = {"CMCI", NULL, NULL},
>> +		[ACPI_HEST_NOTIFY_MCE]      = {"MCE", NULL, NULL},
>> +};
>
> Again, just keep the switch/case statements in the probe and removal
> function and call the init/remove functions directly in them. This is
> much easier.
>
> If we need dynamic registration of handlers (which I don't see yet)
> for the error sources above we could do this with an acpi notify
> handler or so.
>

Without abstraction, notify handler registration seems to be overhead. I 
will modify code as you suggested. Thanks.

Tomasz
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