Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755212AbYGIT37 (ORCPT ); Wed, 9 Jul 2008 15:29:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751304AbYGIT3v (ORCPT ); Wed, 9 Jul 2008 15:29:51 -0400 Received: from rtsoft3.corbina.net ([85.21.88.6]:3315 "EHLO buildserver.ru.mvista.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751272AbYGIT3u (ORCPT ); Wed, 9 Jul 2008 15:29:50 -0400 Date: Wed, 9 Jul 2008 23:29:43 +0400 From: Anton Vorontsov To: Alan Cox Cc: Ingo Molnar , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Steven Rostedt , Daniel Walker Subject: Re: [PATCH v2] serial: 8250: fix shared interrupts issues with SMP and RT kernels Message-ID: <20080709192943.GA12278@polina.dev.rtsoft.ru> Reply-To: avorontsov@ru.mvista.com References: <20080623232957.GA5111@polina.dev.rtsoft.ru> <20080624001221.GA20685@elte.hu> <20080701134343.GA1865@polina.dev.rtsoft.ru> <20080701144353.7285805d@lxorguk.ukuu.org.uk> <20080701150254.GA13390@polina.dev.rtsoft.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Disposition: inline In-Reply-To: <20080701150254.GA13390@polina.dev.rtsoft.ru> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2355 Lines: 72 On Tue, Jul 01, 2008 at 07:02:54PM +0400, Anton Vorontsov wrote: [...] > Signed-off-by: Anton Vorontsov > --- > > On Tue, Jul 01, 2008 at 02:43:53PM +0100, Alan Cox wrote: [...] > > It looks correct to me except that you cannot use spin_lock/disable_irq > > in that way safely. You must always disable_irq before taking the lock, > > or prove it is safe and use disable_irq_nosync > > > > The reason: > > CPU#0 spin_lock_... [taken] > > CPU#1 IRQ > > CPU#1 spin_lock [waits] > > CPU#0 disable_irq (deadlock) > > This deadlock possibility is interesting by itself, thanks for > mentioning it. > > But this can't happen here. IRQ will not grab the up->port.lock, > because port isn't registered in the 8250 IRQ handling chain (yet). Alan, are there any issues with the proof or the patch itself? Thanks, > As for _nosync, probably this is good idea indeed, and should be safe > AFAICS. > > drivers/serial/8250.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c > index 76ccef7..cad0c2d 100644 > --- a/drivers/serial/8250.c > +++ b/drivers/serial/8250.c > @@ -1831,7 +1831,9 @@ static int serial8250_startup(struct uart_port *port) > * the interrupt is enabled. Delays are necessary to > * allow register changes to become visible. > */ > - spin_lock_irqsave(&up->port.lock, flags); > + spin_lock(&up->port.lock); > + if (up->port.flags & UPF_SHARE_IRQ) > + disable_irq_nosync(up->port.irq); > > wait_for_xmitr(up, UART_LSR_THRE); > serial_out_sync(up, UART_IER, UART_IER_THRI); > @@ -1843,7 +1845,9 @@ static int serial8250_startup(struct uart_port *port) > iir = serial_in(up, UART_IIR); > serial_out(up, UART_IER, 0); > > - spin_unlock_irqrestore(&up->port.lock, flags); > + if (up->port.flags & UPF_SHARE_IRQ) > + enable_irq(up->port.irq); > + spin_unlock(&up->port.lock); > > /* > * If the interrupt is not reasserted, setup a timer to > -- > 1.5.5.4 > -- Anton Vorontsov email: cbouatmailru@gmail.com irc://irc.freenode.net/bd2 -- 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/