linux-kernel - Re: device_del() and references

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Message-ID: <20061114112409.GB15340@flint.arm.linux.org.uk>
Date:	Tue, 14 Nov 2006 11:24:09 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Pierre Ossman <drzeus-list@...eus.cx>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: device_del() and references

On Tue, Nov 14, 2006 at 08:40:00AM +0100, Pierre Ossman wrote:
> When a card driver has obtained a reference to a card, what makes sure
> we do not destroy that card from under its feet?

Essentially, the driver model.  (see the answer to your paragraph below.)

> I suspect that device_del() doesn't return until remove() has been
> called and that our requirement is that the card driver must have
> released all references to the card before its remove routine exits.

Your sentence is confusing - which "remove()" are you talking about
here?  If you're talking about mmc_blk_remove() then that's correct.

> If so, then there is the risk of a race in mmc_block. What guarantees
> that the request handler isn't running in parallel with the remove
> function? Again, I suspect that del_gendisk() might grab the queue lock,
> but as there might be stuff left in the queue, this seems insufficient.

Hmm, not sure here.  I think you might be right, but the block layer is
*extremely* finaky when it comes to removing stuff.

In short, I don't know - I've forgotten quite a bit about the low level
block interface with MMC since it's something I did once and only once.

Maybe Jens has some ideas?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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