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

From: Luiz Fernando Capitulino
Date: Wed Nov 23 2005 - 06:36:29 EST

On Tue, 22 Nov 2005 14:13:53 -0800
Greg KH <gregkh@xxxxxxx> 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.


| 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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