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

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Message-Id: <200704062335.26560.bzolnier@gmail.com>
Date:	Fri, 6 Apr 2007 23:35:26 +0200
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Suleiman Souhlal <ssouhlal@...ebsd.org>, 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


On Friday 06 April 2007, Sergei Shtylyov wrote:
> Hello.
> 
> Suleiman Souhlal wrote:

> > The reason the timer could have been active at that point, before applying
> > this patch, is that we try to dispatch a new request after handling one.
> > The new request will then have its own expiry timer, along with a handler.
> > Since  before this patch ide_timer_expiry() only looked at whether or not
> > a handler was present, it would incorrectly think the request had not been
> > handled already, and incorrectly tried to restart the timer.
> 
>     Hm, I'm still not sure why this happens at all, probably need to try 
> reproducing it (unless you post a stack trace :-).

not a stack trace but should explain the issue a bit:

...
ide_timer_expiry
	-> just before taking ide_lock IRQ happens
...
ide_intr
	-> completes the command and queues the next one
...
ide_timer_expiry (resumed)
	-> takes ide_lock
	-> the bug happens ;)

should be even easier to trigger it on SMP since ide_timer_expiry
may be running at the same time as ide_intr

Bart
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