Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750703AbVKWL4a (ORCPT ); Wed, 23 Nov 2005 06:56:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750710AbVKWL43 (ORCPT ); Wed, 23 Nov 2005 06:56:29 -0500 Received: from perninha.conectiva.com.br ([200.140.247.100]:8674 "EHLO perninha.conectiva.com.br") by vger.kernel.org with ESMTP id S1750703AbVKWL42 (ORCPT ); Wed, 23 Nov 2005 06:56:28 -0500 Date: Wed, 23 Nov 2005 09:56:33 -0200 From: Eduardo Pereira Habkost To: Luiz Fernando Capitulino Cc: Greg KH , linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net, akpm@osdl.org Subject: Re: [PATCH 2/2] - usbserial: race-condition fix. Message-ID: <20051123115633.GS14440@duckman.conectiva> References: <20051122195926.18c3221c.lcapitulino@mandriva.com.br> <20051122221353.GA10311@suse.de> <20051123093655.5555f23e.lcapitulino@mandriva.com.br> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="n7zTieg8iIQ1Wja9" Content-Disposition: inline In-Reply-To: <20051123093655.5555f23e.lcapitulino@mandriva.com.br> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2305 Lines: 72 --n7zTieg8iIQ1Wja9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 wrote: >=20 > | On Tue, Nov 22, 2005 at 07:59:26PM -0200, Luiz Fernando Capitulino wrot= e: > | > @@ -60,6 +61,7 @@ struct usb_serial_port { > | > struct usb_serial * serial; > | > struct tty_struct * tty; > | > spinlock_t lock; > | > + struct semaphore sem; > |=20 > | You forgot to document what this semaphore is used for. >=20 > Okay. >=20 > | 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 :) >=20 > 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. >=20 > 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. 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 >=20 > 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. --=20 Eduardo --n7zTieg8iIQ1Wja9 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (GNU/Linux) iD8DBQFDhFjxcaRJ66w1lWgRAv5qAKCDfmBmYby5u7o/jWjGQJoOA0F+XQCfZXvW 86obQtoj2sZvMtmYOI8YKv0= =Q9fM -----END PGP SIGNATURE----- --n7zTieg8iIQ1Wja9-- - 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/