Re: [PATCH 2/2] - usbserial: race-condition fix.

[Greg KH <gregkh@suse.de>]

On Wed, Nov 23, 2005 at 09:36:55AM -0200, Luiz Fernando Capitulino wrote:
> 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.

No, lots of other usb-serial drivers use it.  Increase your grep a bit
wider :)

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

Create a new one for where?

>  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.

I agree, but yet-another-lock isn't the best either.

thanks,

greg k-h
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