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SubjectRe: [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@redhat.com> wrote:
>
> > >From 030af455d4f54482130c8eccb47fe90aaba8808c Mon Sep 17 00:00:00 2001
> > From: John Kacur <jkacur@redhat.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@redhat.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@redhat.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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