Messages in this thread | | | Date | Wed, 23 Nov 2005 10:07:08 -0200 | From | Luiz Fernando Capitulino <> | Subject | Re: [PATCH 2/2] - usbserial: race-condition fix. |
| |
On Wed, 23 Nov 2005 09:56:33 -0200 Eduardo Pereira Habkost <ehabkost@mandriva.com> wrote:
| 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. | > | > Can we drop the spinlock there and use our new semaphore? Or should we | > create a new spinlock just to use there? | | The spin_lock is used only to protect write_urb_busy. An atomic_t seem | to be more appropriate for it. If we do that, I guess we can remove the | (then unused) spinlock.
Ok, but, hmm.. I found the spinklock is actually used by other drivers too.
I didn't catch this before because I wasn't compiling then. Sorry, my fault.
| So we have three proposed changes: | | - Add semaphore to serialize close()/open() (properly documented) | - Replace write_urb_busy with an atomic_t | - Remove the spinlock
Since the spinlock seems to be only used to protect 'write_urb_busy', I agree with those changes.
Greg, do you? If so, I suggested we should add the semaphore first, because it is a bug fix.
I can do the 'write_urb_busy' type replace next week (yes, I will replace all the drivers).
-- Luiz Fernando N. Capitulino - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |