linux-kernel - Re: Possible race condition in usb-serial.c

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Date:	Fri, 22 Dec 2006 11:08:00 -0800 (PST)
From:	J <jhnlmn@...oo.com>
To:	Oliver Neukum <oliver@...kum.org>, Greg KH <gregkh@...e.de>
Cc:	linux-usb-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: Possible race condition in usb-serial.c

> 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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