Date: Wed, 23 Nov 2005 09:36:55 -0200
From: Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>
To: Greg KH <gregkh@suse.de>
Cc: linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net,
       akpm@osdl.org, ehabkost@mandriva.com
Subject: Re: [PATCH 2/2] - usbserial: race-condition fix.
Message-Id: <20051123093655.5555f23e.lcapitulino@mandriva.com.br>
In-Reply-To: <20051122221353.GA10311@suse.de>
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	<20051122221353.GA10311@suse.de>
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On Tue, 22 Nov 2005 14:13:53 -0800
Greg KH <gregkh@suse.de> wrote:

| On Tue, Nov 22, 2005 at 07:59:26PM -0200, Luiz Fernando Capitulino wrote:
| > @@ -60,6 +61,7 @@ struct usb_serial_port {
| >  	struct usb_serial *	serial;
| >  	struct tty_struct *	tty;
| >  	spinlock_t		lock;
| > +	struct semaphore        sem;
| 
| You forgot to document what this semaphore is used for.

 Okay.

| Hm, can we just use the spinlock already present in the port structure
| for this?  Well, drop the spinlock and use the semaphore?  Yeah, that
| means grabbing a semaphore for ever write for some devices, but USB data
| rates are slow enough it wouldn't matter :)

 As far as I read the code, I found that spinlock is only used by the
generic driver, in the
drivers/usb/serial/generic.c:usb_serial_generic_write() function.

 Can we drop the spinlock there and use our new semaphore? Or should we
create a new spinlock just to use there?

 I ask it because the semaphore will be used to serialize open()/close()
operations in the usb-serial driver, is a bit weird to use the same
semaphore in a write() function of other driver.

-- 
Luiz Fernando N. Capitulino
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