Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759083AbZJKMme (ORCPT ); Sun, 11 Oct 2009 08:42:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754570AbZJKMmd (ORCPT ); Sun, 11 Oct 2009 08:42:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8359 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753324AbZJKMmc (ORCPT ); Sun, 11 Oct 2009 08:42:32 -0400 Date: Sun, 11 Oct 2009 14:41:15 +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: <20091011113317.GA4901@nowhere> 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: 4947 Lines: 151 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 -- 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/