Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752228AbZJKV1J (ORCPT ); Sun, 11 Oct 2009 17:27:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751985AbZJKV1G (ORCPT ); Sun, 11 Oct 2009 17:27:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58478 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751958AbZJKV1F (ORCPT ); Sun, 11 Oct 2009 17:27:05 -0400 Date: Sun, 11 Oct 2009 23:25:43 +0200 (CEST) From: John Kacur X-X-Sender: jkacur@localhost.localdomain To: Frederic Weisbecker cc: Alan Cox , linux-kernel@vger.kernel.org, Thomas Gleixner , Jonathan Corbet , Peter Zijlstra , Christoph Hellwig , Andrew Morton , Vincent^M^J Sanders , Ingo Molnar Subject: Re: [PATCH] sound_core.c: Remove BKL from soundcore_open In-Reply-To: Message-ID: References: <20091011004219.74c30f67@lxorguk.ukuu.org.uk> <20091011113317.GA4901@nowhere> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5623 Lines: 167 On Sun, 11 Oct 2009, John Kacur wrote: > > > On Sun, 11 Oct 2009, Frederic Weisbecker wrote: > > > On Sun, Oct 11, 2009 at 02:25:53AM +0200, John Kacur wrote: > > > > > > > > > On Sun, 11 Oct 2009, Alan Cox wrote: > > > > > > > On Sun, 11 Oct 2009 01:24:14 +0200 (CEST) > > > > John Kacur wrote: > > > > > > > > > >From 030af455d4f54482130c8eccb47fe90aaba8808c Mon Sep 17 00:00:00 2001 > > > > > From: John Kacur > > > > > Date: Sat, 10 Oct 2009 23:39:56 +0200 > > > > > Subject: [PATCH] This code is already protected by spin_lock, and doesn't require the bkl > > > > > > > > Sorry but I don't think that is true becaue of: > > > > > > > > spin_unlock(&sound_loader_lock); > > > > if(file->f_op->open) > > > > err = file->f_op->open(inode,file); > > > > > > > > > > > > So the underlying driver open method expects lock_kernel status and you > > > > don't propogate it down. You really need to track down each thing that > > > > can be called into here and fix it, or maybe just punt for the moment and > > > > push it down to > > > > > > > > { > > > > lock_kernel() > > > > err = file-f_op->open ... > > > > unlock_kernel() > > > > } > > > > > > > > so its obvious to the next person who takes up the war on the BKL what is > > > > to be tackled. > > > > > > > > > > Yikes, I missed that. Still I'm loath to just push it down like that. I > > > wonder if I can use a mutex there. What about the following patch? > > > > > > From 8b0b91523ee2fcf60ccd82dba44b8da8bad34ce4 Mon Sep 17 00:00:00 2001 > > > From: John Kacur > > > Date: Sun, 11 Oct 2009 02:14:44 +0200 > > > Subject: [PATCH] Remove the bkl in soundcore_open > > > > > > Remove the bkl in soundcore_open since it is mostly covered by the sound_loader_lock spin_lock > > > > > > Protect the underlying driver open method with a mutex. > > > > > > Signed-off-by: John Kacur > > > --- > > > sound/sound_core.c | 8 ++++---- > > > 1 files changed, 4 insertions(+), 4 deletions(-) > > > > > > diff --git a/sound/sound_core.c b/sound/sound_core.c > > > index 49c9981..6afb6f1 100644 > > > --- a/sound/sound_core.c > > > +++ b/sound/sound_core.c > > > @@ -14,6 +14,8 @@ > > > #include > > > #include > > > > > > +static DEFINE_MUTEX(osc_mutex); > > > + > > > #ifdef CONFIG_SOUND_OSS_CORE > > > static int __init init_oss_soundcore(void); > > > static void cleanup_oss_soundcore(void); > > > @@ -576,8 +578,6 @@ static int soundcore_open(struct inode *inode, struct file *file) > > > struct sound_unit *s; > > > const struct file_operations *new_fops = NULL; > > > > > > - lock_kernel (); > > > - > > > chain=unit&0x0F; > > > if(chain==4 || chain==5) /* dsp/audio/dsp16 */ > > > { > > > @@ -631,17 +631,17 @@ static int soundcore_open(struct inode *inode, struct file *file) > > > file->f_op = new_fops; > > > spin_unlock(&sound_loader_lock); > > > if(file->f_op->open) > > > + mutex_lock(&osc_mutex); > > > err = file->f_op->open(inode,file); > > > + mutex_unlock(&osc_mutex); > > > > > > Yeah that's tempting, but I fear that also means this mutex will > > never be removed.... > > > > Sigh... I do see your point - but on the otherhand if measurements don't > show that mutex as being too coarse grained, then is it a problem? > > Never-the-less here is version 3 of the patch - like Alan suggested, > punting, but at least reducing the area covered by the BKL. > From ac9bdbdd192149e2498b6e16dc71f0a3933e1554 Mon Sep 17 00:00:00 2001 > From: John Kacur > Date: Sun, 11 Oct 2009 14:25:46 +0200 > Subject: [PATCH] soundcore_open: Reduce the area BKL coverage in this function. > > Most of this function is protected by the sound_loader_lock. > We can push down the BKL to this call out err = file->f_op->open(inode,file); > > Signed-off-by: John Kacur > --- > sound/sound_core.c | 6 ++---- > 1 files changed, 2 insertions(+), 4 deletions(-) > > diff --git a/sound/sound_core.c b/sound/sound_core.c > index 49c9981..a7d6956 100644 > --- a/sound/sound_core.c > +++ b/sound/sound_core.c > @@ -576,8 +576,6 @@ static int soundcore_open(struct inode *inode, struct file *file) > struct sound_unit *s; > const struct file_operations *new_fops = NULL; > > - lock_kernel (); > - > chain=unit&0x0F; > if(chain==4 || chain==5) /* dsp/audio/dsp16 */ > { > @@ -631,17 +629,17 @@ static int soundcore_open(struct inode *inode, struct file *file) > file->f_op = new_fops; > spin_unlock(&sound_loader_lock); > if(file->f_op->open) > + lock_kernel(); > err = file->f_op->open(inode,file); > + unlock_kernel(); > if (err) { > fops_put(file->f_op); > file->f_op = fops_get(old_fops); > } > fops_put(old_fops); > - unlock_kernel(); > return err; > } > spin_unlock(&sound_loader_lock); > - unlock_kernel(); > return -ENODEV; > } > > -- > 1.6.0.6 > @Alan Are you okay with this 3rd version of the patch that pushes the bkl lock further down into the function so that it is only around the err = file->f_op->open(inode,file); Not ideal - but an improvement and step in the right direction. If so, maybe I can get an ack, so that Thomas might include it in his new kill-the-bkl tree. Thanks -- 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/