linux-kernel - Re: [PATCH] sound_core.c: Remove BKL from soundcore

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Message-ID: <alpine.LFD.2.00.0910110223510.4921@localhost.localdomain>
Date:	Sun, 11 Oct 2009 02:25:53 +0200 (CEST)
From:	John Kacur <jkacur@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Corbet <corbet@....net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vincent^M^J Sanders <vince@...tec.co.uk>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sound_core.c: Remove BKL from soundcore_open



On Sun, 11 Oct 2009, Alan Cox wrote:

> On Sun, 11 Oct 2009 01:24:14 +0200 (CEST)
> John Kacur <jkacur@...hat.com> wrote:
> 
> > >From 030af455d4f54482130c8eccb47fe90aaba8808c Mon Sep 17 00:00:00 2001
> > From: John Kacur <jkacur@...hat.com>
> > 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 <jkacur@...hat.com>
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 <jkacur@...hat.com>
---
 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 <linux/major.h>
 #include <sound/core.h>
 
+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);
 		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

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