linux-kernel - Re: pktcdvd oops

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Message-ID: <Pine.LNX.4.64.0711072303080.6991@quad.localdomain>
Date:	Wed, 7 Nov 2007 23:06:47 +0100 (CET)
From:	Peter Osterlund <petero2@...ia.com>
To:	Tejun Heo <htejun@...il.com>
cc:	Thomas Maier <balagi@...tmail.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, gregkh@...e.de
Subject: Re: pktcdvd oops

On Wed, 7 Nov 2007, Tejun Heo wrote:

> Peter Osterlund wrote:
>> If the
>> __module_get() is not safe because the module code could have already
>> been unloaded, how can it possibly be made safe by adding more code to
>> the pktcdvd module? If the module is unloaded, trying to execute its
>> code can't be a good thing no matter what the code does.
>
> sysfs itself is now out of module lifespan rules.  sysfs callbacks are
> guaranteed to stay in memory while running by sysfs node removal waiting
> for completion of in-flight operations before returning.  In pktcdvd's
> case, class_destroy() call in pkt_sysfs_cleanup() will wait for all
> in-flight sysfs r/w ops to complete.
>
> So, even while sysfs callbacks are executing, the module beneath can die
> but it will stay in memory till all the callbacks return.  You need to
> test module liveness using try_module_get() (and it can fail) if you
> want to grab module reference from sysfs callbacks.

Thanks for the explanation.

Given that explanation, I think the patch is correct and it does fix the 
BUG on my computer. Can you please push it upstream?

In any case:

Acked-by: Peter Osterlund <petero2@...ia.com>

-- 
Peter Osterlund - petero2@...ia.com
http://web.telia.com/~u89404340
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