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Date: Thu, 4 Mar 2010 09:32:03 +0000
Message-ID: <9b2b86521003040132v168399ct9241f3ad9ff8c4c7@mail.gmail.com>
Subject: Re: [Resend][PATCH] ACPI / EC: Remove race between EC driver and 
	suspend process (rev. 3)
From: Alan Jenkins <sourcejedi.lkml@googlemail.com>
To: Len Brown <lenb@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
       Alexey Starikovskiy <astarikovskiy@suse.de>,
       ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
       pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Maxim Levitsky <maximlevitsky@gmail.com>
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On 3/4/10, Len Brown <lenb@kernel.org> wrote:
> Isn't the problem at hand that the boot-kernel stops
> in mid-transaction, and the resumed hibernate image
> then blunders forward with its first transaction
> only to find the EC in an intermediate state?
>
> If yes, I then making the transaction atomic WRT
> the boot kernel stopping should fix the problem.
>
> The patch sets a FROZEN bit, and subsequent
> requests for EC transactions simply fail.
> How do we know that we set the bit at the right time?
> What transactions or parts of transactions will fail,
> and what are the consequences of those failures?

The problem transactions on my machine were probably started by
ec_check_sci().  I.e. QUERY transactions which read the value of an
event raised by the EC.  (I triggered the problem by pressing ACPI
hotkeys, although I haven't been able to reproduce it since).

That might explain why the transactions can be asynchronous with the
s2disk task - because these transactions are run in the ACPI
workqueue.  Perhaps the workqueue needs to be flushed after the EC GPE
is disabled?

Alan