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Date: Wed, 20 Dec 2006 11:32:31 -0800 (PST)
From: J <jhnlmn@yahoo.com>
Subject: Re: Possible race condition in usb-serial.c
To: linux-kernel@vger.kernel.org
In-Reply-To: <200612201047.20842.oliver@neukum.org>
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Thank you for the explanation.

> serial_close is safe because serial_disconnect
> lowers the refcount

Sorry, I meant serial_open, as in my original example.

I am currently trying to fix a legacy 2.4 based USB
driver and I am having various races, 
serial_open/usb_serial_disconnect is the most lively.
I am not asking your help in fixing this old 2.4 junk
(in fact I already fixed it using a global semaphore
to protect serial_table).

But I still want to understand how the latest and
greatest 2.6 driver is supposed to work so I can
adopt some of the changes. At first I thought that
the ref-counting will help, but then found that 
it does not fix much! The race is as lively 
as ever.

Also I found that BKL/lock_kernel is compiled out in
my configuration because it is not an SMP build.

I see that in 2.6 BKL/lock_kernel are also optional
for non-SMP builds. Is it true?
If yes, then again, how this is supposed to work
and avoid races?


Thank you
John


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