linux-kernel - Re: [PATCH] Correctly prevent IDE timer expiry function to run if request was already handled

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Message-ID: <46169DDA.6020008@ru.mvista.com>
Date:	Fri, 06 Apr 2007 23:22:02 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Suleiman Souhlal <ssouhlal@...ebsd.org>
CC:	bzolnier@...il.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Correctly prevent IDE timer expiry function to run if
 request was already handled

Hello.

Suleiman Souhlal wrote:

> It is possible for the timer expiry function to run even though the
> request has already been handled: ide_timer_expiry() only checks that
> the handler is not NULL, but it is possible that we have handled a
> request (thus clearing the handler) and then started a new request
> (thus starting the timer again, and setting a handler). 

> A simple way to exhibit this is to set the DMA timeout to 1 jiffy and
> run dd: The kernel will panic after a few minutes because
> ide_timer_expiry() tries to add a timer when it's already active.

> To fix this, we simply add a request generation count that gets
> incremented at every interrupt, and check in ide_timer_expiry() that
> we have not already handled a new interrupt before running the expiry
> function.

    Couldn't this be addressed by simply changing add_timer() to mod_timer()?

MBR, Sergei
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