linux-kernel - Re: [RESEND PATCH v3 3/9] EDAC/ghes: Make ghes_edac a proper module to remove the dependency on ghes

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Message-ID: <YwZFqHvcEzVpAxzn@zn.tnic>
Date:   Wed, 24 Aug 2022 17:37:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jia He <justin.he@....com>
Cc:     Len Brown <lenb@...nel.org>, James Morse <james.morse@....com>,
        Tony Luck <tony.luck@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Richter <rric@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Jonathan Corbet <corbet@....net>,
        Jan Luebbe <jlu@...gutronix.de>,
        Khuong Dinh <khuong@...amperecomputing.com>,
        Kani Toshi <toshi.kani@....com>,
        Ard Biesheuvel <ardb@...nel.org>, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        devel@...ica.org, "Rafael J . Wysocki" <rafael@...nel.org>,
        Shuai Xue <xueshuai@...ux.alibaba.com>,
        Jarkko Sakkinen <jarkko@...nel.org>, linux-efi@...r.kernel.org,
        nd@....com, "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Muchun Song <songmuchun@...edance.com>,
        linux-doc@...r.kernel.org, stable@...nel.org
Subject: Re: [RESEND PATCH v3 3/9] EDAC/ghes: Make ghes_edac a proper module
 to remove the dependency on ghes

On Mon, Aug 22, 2022 at 03:40:42PM +0000, Jia He wrote:
> Commit dc4e8c07e9e2 ("ACPI: APEI: explicit init of HEST and GHES in
> apci_init()") introduced a bug that ghes_edac_register() would be invoked
> before edac_init(). Because at that time, the bus "edac" hadn't been even
> registered, this created sysfs /devices/mc0 instead of
> /sys/devices/system/edac/mc/mc0 on an Ampere eMag server.
> 
> To remove the dependency of ghes_edac on ghes, make it a proper module. Use
> a list to save the probing devices in ghes_probe(), and defer the
> ghes_edac_register() to module_init() of the new ghes_edac module by
> iterating over the devices list.
> 
> Co-developed-by: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Jia He <justin.he@....com>
> Fixes: dc4e8c07e9e2 ("ACPI: APEI: explicit init of HEST and GHES in apci_init()")
> Cc: stable@...nel.org

Why is this marked for stable?

The prerequisite patches are needed too. I guess this needs to be
communicated to stable folks somehow by doing

Cc: stable@...nel.org # needs commits X, Y, ...

but I guess the committer needs to do that because only at commit time
will X and Y be known...

So, is there any particular reason why this should be in stable?

> @@ -1442,7 +1449,9 @@ static int ghes_remove(struct platform_device *ghes_dev)
>  
>  	ghes_fini(ghes);
>  
> -	ghes_edac_unregister(ghes);
> +	mutex_lock(&ghes_devs_mutex);
> +	list_del_rcu(&ghes->elist);

Is that list RCU-protected?

> +	mutex_unlock(&ghes_devs_mutex);
>  
>  	kfree(ghes);

...

> @@ -566,3 +549,35 @@ void ghes_edac_unregister(struct ghes *ghes)
>  unlock:
>  	mutex_unlock(&ghes_reg_mutex);
>  }
> +
> +static int __init ghes_edac_init(void)
> +{
> +	struct ghes *g, *g_tmp;
> +
> +	if (!IS_ENABLED(CONFIG_X86))
> +		force_load = true;

No, this is not how this works.

> +	ghes_devs = ghes_get_devices(force_load);
> +	if (!ghes_devs)
> +		return -ENODEV;

You simply need to check force_load here.

> +	list_for_each_entry_safe(g, g_tmp, ghes_devs, elist) {
> +		ghes_edac_register(g->dev);
> +	}
> +
> +	return 0;
> +}

-- 
Regards/Gruss,
    Boris.

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