Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754233Ab0AEHok (ORCPT ); Tue, 5 Jan 2010 02:44:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753480Ab0AEHoj (ORCPT ); Tue, 5 Jan 2010 02:44:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59359 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750768Ab0AEHoj (ORCPT ); Tue, 5 Jan 2010 02:44:39 -0500 Date: Tue, 5 Jan 2010 00:43:44 -0700 From: Pete Zaitcev To: Stefani Seibold Cc: Johan Hovold , Andrew Morton , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: USB: serial: kfifo_len locking Message-ID: <20100105004344.082bb69f@redhat.com> In-Reply-To: <1262632804.4814.17.camel@wall-e> References: <20100104174352.GA26606@localhost> <1262632804.4814.17.camel@wall-e> Organization: Red Hat, Inc. Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2702 Lines: 68 On Mon, 04 Jan 2010 20:20:04 +0100 Stefani Seibold wrote: > Am Montag, den 04.01.2010, 18:43 +0100 schrieb Johan Hovold: > > I noticed that the locking that used to protect kfifo_len in > > usb_serial_generic_chars_in_buffer was removed when the kifo api changed > > to not use internal locking (c1e13f25674ed564948ecb7dfe5f83e578892896 -- > > kfifo: move out spinlock). > > > > Was this intentional? > > > > Yes, the locking is not necessary until only one reader and one writer > is using the fifo. If you don't trust this you can apply this patch: > > --- linux-2.6.33-rc2.orig/drivers/usb/serial/generic.c 2009-12-27 23:37:03.566060210 +0100 > +++ linux-2.6.33-rc2.new/drivers/usb/serial/generic.c 2010-01-04 20:15:38.023351711 +0100 > @@ -386,12 +386,12 @@ int usb_serial_generic_chars_in_buffer(s > > dbg("%s - port %d", __func__, port->number); > > - if (serial->type->max_in_flight_urbs) { > - spin_lock_irqsave(&port->lock, flags); > + spin_lock_irqsave(&port->lock, flags); > + if (serial->type->max_in_flight_urbs) > chars = port->tx_bytes_flight; > - spin_unlock_irqrestore(&port->lock, flags); > - } else if (serial->num_bulk_out) > + else if (serial->num_bulk_out) > chars = kfifo_len(&port->write_fifo); > + spin_unlock_irqrestore(&port->lock, flags); > > Then everything kfifo_... access in the usb serial is handled with an > active spinlock. This actually was a side effect of the "byte lost on close" patch that I submitted, it should be in Greg's tree. The relevant part goes like this: diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c index f1ea3a3..3372faa 100644 --- a/drivers/usb/serial/generic.c +++ b/drivers/usb/serial/generic.c @@ -386,12 +386,15 @@ int usb_serial_generic_chars_in_buffer(struct tty_struct *tty) dbg("%s - port %d", __func__, port->number); + spin_lock_irqsave(&port->lock, flags); if (serial->type->max_in_flight_urbs) { - spin_lock_irqsave(&port->lock, flags); chars = port->tx_bytes_flight; - spin_unlock_irqrestore(&port->lock, flags); - } else if (serial->num_bulk_out) - chars = kfifo_len(&port->write_fifo); + } else if (serial->num_bulk_out) { + /* This overcounts badly, but is good enough for drain wait. */ + chars = __kfifo_len(port->write_fifo); + chars += port->write_urb_busy * port->bulk_out_size; + } + spin_unlock_irqrestore(&port->lock, flags); dbg("%s - returns %d", __func__, chars); return chars; -- 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/