linux-kernel - Re: [PATCH v2 4/7] ghes_edac: avoid multiple calls to dmi

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Date:   Mon, 14 Aug 2017 19:02:15 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "bp@...en8.de" <bp@...en8.de>
CC:     "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 4/7] ghes_edac: avoid multiple calls to dmi_walk()

On Mon, 2017-08-14 at 20:35 +0200, Borislav Petkov wrote:
> On Mon, Aug 14, 2017 at 06:17:47PM +0000, Kani, Toshimitsu wrote:
> > Right, ghes_edac_report_mem_error() gets serialized per a GHES
> > entry, but not globally.
> 
> Globally what?

GHES v2's ACK is not a global lock.  So, it does not guarantee that
ghes_edac_report_mem_error() never gets called concurrently.

> What is the actual potential scenario for concurrency issues you see?
> Example pls.

ghes_probe() supports multiple sources defined in
acpi_hest_notify_types.  Say, there are two entries for memory errors,
one with ACPI_HEST_NOTIFY_EXTERNAL and the other with
ACPI_HEST_NOTIFY_SCI.  They may report errors independently.  While
ghes_edac_report_mem_error() is being called from the SCI, it can be
called from the ext interrupt at a same time.

I do not know how likely we see such case, but the code should be
written according to the spec.

Thanks,
-Toshi