linux-kernel - Re: [PATCH]bluetooth rfcomm

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Date:	Wed, 7 Nov 2007 09:20:33 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Marcel Holtmann" <marcel@...tmann.org>
Cc:	linux-kernel@...r.kernel.org, bluez-devel@...ts.sf.net
Subject: Re: [PATCH]bluetooth rfcomm_dev refcount bug fix

On Nov 6, 2007 9:33 PM, Marcel Holtmann <marcel@...tmann.org> wrote:
> Hi Dave,
>
> > I'm afraid to be considered as spam ;)
> >
> > (Due to timezone offset, I have to mail again and cann't wait for your
> > reply, sorry for the annoying)
>
> I am in a different timezone every other week. So nevermind ;)
>
> > I think the rfcomm_dev_put could be seperated from the rfcomm_dev_put,
> > it will be more straitforward then.
> >
> > please consider below patch, tested on my side. thanks.
>
> That one looks totally wrong to me. Without even testing it, it will
> have side effects that you haven't run into yet. Unless the TTY core
> changed so much, this comments are there for a really good reason and
> the code is tested a lot.
What side effects?

Anyway, the refcnt is wrong in rfcomm_release_dev. We could either
remove the rfcomm_dev_del in rfcomm_tty_hangup or remove the
rfcomm_dev_put in the end of rfcomm_release_dev, or the rfcomm_dev
will be destructed, and  the later callback of rfcomm_tty_close could
cause oops.

>
> Also if you have to do two rfcomm_dev_put() in a row, then we are doing
> something really wrong and this tries to hide a real bug somewhere.
One is for device deletion (1->0), one is for the get/put pairs,
actually same as before.

Main reason of doing so in this patch is that if I remove the last
rfcomm_dev_put in rfcomm_release_dev, then it looks like get device
<-->  del device, so relace it with set deletion flag and then put
the device like "get device <--> put device" which is straitforward.

>
> Regards
>
> Marcel
>
>
>
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