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Date: Fri, 22 Dec 2006 11:08:00 -0800 (PST)
From: J <jhnlmn@yahoo.com>
Subject: Re: Possible race condition in usb-serial.c
To: Oliver Neukum <oliver@neukum.org>, Greg KH <gregkh@suse.de>
Cc: linux-usb-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
In-Reply-To: <200612221914.41111.oliver@neukum.org>
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> This problem will need some deeper surgery probably
> involving
> removal of the refcounting.

Refcounting may be OK if used consistently. 
It is not OK when some pointers are ref-counted, 
but other (in serial_table) are not (like it is
in the current version).

As for the deeper surgery, what do you think about my
earlier suggestion to start by rewriting
usb_serial_probe
to fully initialize usb_serial before it is added to 
serial_table? 

So, instead of the current:
1. create_serial
...
2. mutex_lock(&table_lock);
3. get_free_serial (which inserts serial to
serial_table)
...
4. initializes serial
5. mutex_unlock(&table_lock);

we will get:

1. create_serial
2. initializes serial

3. add_serial_toserial_table  (with internal mutex
lock if needed)

Similar approach should be used in other places to
minimize the code executed under the mutex.

John

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