netdev - QUESTION: How to fix race between .suspend routine and watchdog timer

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Message-Id: <200710250612.44296.maximlevitsky@gmail.com>
Date:	Thu, 25 Oct 2007 06:12:44 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-pm@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: QUESTION: How to fix race between .suspend routine and watchdog timer

Hi,

Recently, trying to fix saa7134 suspend/resume problems I found that there 
is a race between IRQ handler and .suspend , and that I cant let driver access the device
while its in D3 since it can lock up some systems.

Now I am looking to fix those issues in two drivers that have my .suspend/.resume routines.
the saa7134 capture chip and dmfe, the davicom network driver.

Looking through the dmfe code, I noticed yet another possible race.
A race between the .suspend, and a timer that serves both as a watchdog, and link state detector.
Again I need to prevent it from running during the suspend/resume, but how?

I can use del_timer in .suspend, and mod_timer in .resume, but that doesn't protect against
race with already running timer.
I can use del_timer_sync, but it states that it is useless if timer re-enables itself, and I agree with that.
In dmfe case the timer does re-enable itself.

I can put checks in the timer for ->insuspend, and don't re enable it if set,
but that opens a new can of worms with memory barriers, etc...

So please tell me how properly to do that.

By the way, this problem, together with synchronize_irq it very generic, since most drivers
have and irq handler, and a timeout timer.

Best regards,
	Maxim Levitsky
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