From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752956AbaCaEKX (ORCPT ); Mon, 31 Mar 2014 00:10:23 -0400 Received: from [216.32.181.181] ([216.32.181.181]:8416 "EHLO ch1outboundpool.messaging.microsoft.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1750976AbaCaEKU (ORCPT ); Mon, 31 Mar 2014 00:10:20 -0400 X-Forefront-Antispam-Report: CIP:70.37.183.190;KIP:(null);UIP:(null);IPV:NLI;H:mail.freescale.net;RD:none;EFVD:NLI X-SpamScore: -5 X-BigFish: VS-5(zzbb2dI98dI9371I936eI1432Izz1f42h2148h208ch1ee6h1de0h1fdah2073h2146h1202h1e76h2189h1d1ah1d2ah21bch1fc6hzz1de098h8275bh1de097hz2dh2a8h839h947hd25he5bhf0ah1288h12a5h12a9h12bdh137ah13b6h1441h1504h1537h153bh162dh1631h1758h1765h18e1h190ch1946h19b4h19c3h1ad9h1b0ah1b2fh2222h224fh1fb3h1d0ch1d2eh1d3fh1dfeh1dffh1f5fh1fe8h1ff5h209eh22d0h2336h2438h2461h2487h24ach24d7h2516h2545h255eh25cch25f6h2605h268bh1155h) Message-ID: <5338EA57.1000509@freescale.com> Date: Mon, 31 Mar 2014 12:08:55 +0800 From: Hongbo Zhang User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: Vinod Koul CC: Vinod Koul , , , , , , Subject: Re: [PATCH 6/7] DMA: Freescale: use spin_lock_bh instead of spin_lock_irqsave References: <1389851246-8564-1-git-send-email-hongbo.zhang@freescale.com> <1389851246-8564-7-git-send-email-hongbo.zhang@freescale.com> <1395817294.6569.2.camel@vkoul-udesk3> <533517C1.8080208@freescale.com> <20140329134528.GQ1976@intel.com> In-Reply-To: <20140329134528.GQ1976@intel.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-OriginatorOrg: freescale.com X-FOPE-CONNECTOR: Id%0$Dn%*$RO%0$TLS%0$FQDN%$TlsDn% X-FOPE-CONNECTOR: Id%0$Dn%FREESCALE.MAIL.ONMICROSOFT.COM$RO%1$TLS%0$FQDN%$TlsDn% Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/29/2014 09:45 PM, Vinod Koul wrote: > On Fri, Mar 28, 2014 at 02:33:37PM +0800, Hongbo Zhang wrote: >> On 03/26/2014 03:01 PM, Vinod Koul wrote: >>> On Thu, 2014-01-16 at 13:47 +0800, hongbo.zhang@freescale.com wrote: >>>> From: Hongbo Zhang >>>> >>>> The usage of spin_lock_irqsave() is a stronger locking mechanism than is >>>> required throughout the driver. The minimum locking required should be used >>>> instead. Interrupts will be turned off and context will be saved, it is >>>> unnecessary to use irqsave. >>>> >>>> This patch changes all instances of spin_lock_irqsave() to spin_lock_bh(). All >>>> manipulation of protected fields is done using tasklet context or weaker, which >>>> makes spin_lock_bh() the correct choice. >>>> > >>>> /** >>>> @@ -1124,11 +1120,10 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data) >>>> static void dma_do_tasklet(unsigned long data) >>>> { >>>> struct fsldma_chan *chan = (struct fsldma_chan *)data; >>>> - unsigned long flags; >>>> chan_dbg(chan, "tasklet entry\n"); >>>> - spin_lock_irqsave(&chan->desc_lock, flags); >>>> + spin_lock_bh(&chan->desc_lock); >>> okay here is the problem :( >>> >>> You moved to _bh variant. So if you grab the lock in rest of the code >>> and irq gets triggered then here we will be spinning to grab the lock. >>> So effectively you made right locking solution into deadlock situation! >> If the rest code grabs lock by spin_lock_bh(), and if irq raised, >> the tasklet could not be executed because it has been disabled by >> the _bh variant function. > yes if you are accessing resources only in tasklet and rest of the code, then > _bh variant works well. The problem here is usage in irq handler > The name dma_do_tasklet may mislead, it is tasklet handler, not irq handler, not a trigger to load tasklet. the irq handler is fsldma_chan_irq, and I don't use lock in it. If it is the problem, I would like to change dma_do_tasklet to dma_tasklet to eliminate misleading.