Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751968AbaBGJrv (ORCPT ); Fri, 7 Feb 2014 04:47:51 -0500 Received: from smtp-vbr1.xs4all.nl ([194.109.24.21]:4419 "EHLO smtp-vbr1.xs4all.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751356AbaBGJrt (ORCPT ); Fri, 7 Feb 2014 04:47:49 -0500 Message-ID: <52F4ABA2.5000905@xs4all.nl> Date: Fri, 07 Feb 2014 10:47:14 +0100 From: Hans Verkuil User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131103 Icedove/17.0.10 MIME-Version: 1.0 To: Arnd Bergmann CC: linux-kernel@vger.kernel.org, Mauro Carvalho Chehab , linux-media@vger.kernel.org Subject: Re: [PATCH, RFC 07/30] [media] radio-cadet: avoid interruptible_sleep_on race References: <1388664474-1710039-1-git-send-email-arnd@arndb.de> <1388664474-1710039-8-git-send-email-arnd@arndb.de> <52D90A2F.2030903@xs4all.nl> <201401171528.02016.arnd@arndb.de> <52F4A82C.7010104@xs4all.nl> In-Reply-To: <52F4A82C.7010104@xs4all.nl> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/07/2014 10:32 AM, Hans Verkuil wrote: > Hi Arnd! > > On 01/17/2014 03:28 PM, Arnd Bergmann wrote: >> On Friday 17 January 2014, Hans Verkuil wrote: >>>> @@ -323,25 +324,32 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo >>>> struct cadet *dev = video_drvdata(file); >>>> unsigned char readbuf[RDS_BUFFER]; >>>> int i = 0; >>>> + DEFINE_WAIT(wait); >>>> >>>> mutex_lock(&dev->lock); >>>> if (dev->rdsstat == 0) >>>> cadet_start_rds(dev); >>>> - if (dev->rdsin == dev->rdsout) { >>>> + while (1) { >>>> + prepare_to_wait(&dev->read_queue, &wait, TASK_INTERRUPTIBLE); >>>> + if (dev->rdsin != dev->rdsout) >>>> + break; >>>> + >>>> if (file->f_flags & O_NONBLOCK) { >>>> i = -EWOULDBLOCK; >>>> goto unlock; >>>> } >>>> mutex_unlock(&dev->lock); >>>> - interruptible_sleep_on(&dev->read_queue); >>>> + schedule(); >>>> mutex_lock(&dev->lock); >>>> } >>>> + >>> >>> This seems overly complicated. Isn't it enough to replace interruptible_sleep_on >>> by 'wait_event_interruptible(&dev->read_queue, dev->rdsin != dev->rdsout);'? >>> >>> Or am I missing something subtle? >> >> The existing code sleeps with &dev->lock released because the cadet_handler() >> function needs to grab (and release) the same lock before it can wake up >> the reader thread. >> >> Doing the simple wait_event_interruptible() would result in a deadlock here. > > I don't see it. I propose this patch: > > Signed-off-by: Hans Verkuil > > diff --git a/drivers/media/radio/radio-cadet.c b/drivers/media/radio/radio-cadet.c > index 545c04c..2f658c6 100644 > --- a/drivers/media/radio/radio-cadet.c > +++ b/drivers/media/radio/radio-cadet.c > @@ -327,13 +327,15 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo > mutex_lock(&dev->lock); > if (dev->rdsstat == 0) > cadet_start_rds(dev); > - if (dev->rdsin == dev->rdsout) { > + while (dev->rdsin == dev->rdsout) { > if (file->f_flags & O_NONBLOCK) { > i = -EWOULDBLOCK; > goto unlock; > } > mutex_unlock(&dev->lock); > - interruptible_sleep_on(&dev->read_queue); > + if (wait_event_interruptible(&dev->read_queue, Oops, that's without an '&' before dev->read_queue. I forgot to update my patch before posting, sorry about that. Hans > + dev->rdsin != dev->rdsout)) > + return -EINTR; > mutex_lock(&dev->lock); > } > while (i < count && dev->rdsin != dev->rdsout) > > Tested with my radio-cadet card. > > This looks good to me. If I am still missing something, let me know! > > Regards, > > Hans > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/