linux-kernel - Re: [Resend][PATCH] ACPI / EC: Remove race between EC driver and suspend process (rev. 3)

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Message-ID: <9b2b86521003040132v168399ct9241f3ad9ff8c4c7@mail.gmail.com>
Date:	Thu, 4 Mar 2010 09:32:03 +0000
From:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
To:	Len Brown <lenb@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Maxim Levitsky <maximlevitsky@...il.com>
Subject: Re: [Resend][PATCH] ACPI / EC: Remove race between EC driver and 
	suspend process (rev. 3)

On 3/4/10, Len Brown <lenb@...nel.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
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