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