Re: [PATCH] sound_core.c: Remove BKL from soundcore_open

From: Frederic Weisbecker
Date: Sun Oct 11 2009 - 07:35:00 EST


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 <jkacur@xxxxxxxxxx> wrote:
> >
> > > >From 030af455d4f54482130c8eccb47fe90aaba8808c Mon Sep 17 00:00:00 2001
> > > From: John Kacur <jkacur@xxxxxxxxxx>
> > > 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@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> ---
> 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);


Yeah that's tempting, but I fear that also means this mutex will
never be removed....

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