linux-kernel - Re: [PATCH] fb: move mutex_init to framebuffer

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Message-Id: <1247046145.22324.12.camel@falcon>
Date:	Wed, 08 Jul 2009 17:42:25 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	Daniel Mack <daniel@...aq.de>
Cc:	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Rafael J. Wysocki" <rjw@...k.pl>, stable@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] fb: move mutex_init to framebuffer_alloc()

On Wed, 2009-07-01 at 18:26 +0200, Daniel Mack wrote:
> In 537a1bf05, a per-fbinfo mutex was added and framebuffer drivers were
> adopted accordingly. This new lock is currently initialized in
> register_framebuffer().
> 
> The mx3fb driver takes this lock in mx3fb_map_video_memory() _before_
> register_framebuffer() is called and hence crashes the system very
> early.
> 
> Moving this mutex_init() to framebuffer_alloc() solves this and also
> seems a lot more straight forward.
> 

but this may introduce deadlock to some _old_ drivers which have not
used framebuffer_alloc to allocate fb_info structure.

to avoid deadlock, these drivers need to change kmalloc to
framebuffer_alloc, otherwise, they need to add their own mutexes
initialization source code:
		mutex_init(&info->lock);	mutex_init(&info->mm_lock);

here is only a record for the _old_ drivers' maintainers. hope they can
get this info from google or find this commit: 

commit 4148df9b0f38bdd362dd91d52076926c11cbe5a9
Author: Paul Mundt <lethal@...ux-sh.org>
Date:   Mon Jul 6 00:25:57 2009 +0900

    fb: Initialize fb_info mutexes in framebuffer_alloc()
    
    This way they'll be properly initialized early enough for users that
may
    touch them before the framebuffer has been registered.
    
    Drivers that allocate their fb_info structure some other way (like
    matrocfb's broken static allocation) need to be fixed up
appropriately.
    
    Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
    Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

Regards,
Wu Zhangjin

> Signed-off-by: Daniel Mack <daniel@...aq.de>
> Cc:: Krzysztof Helt <krzysztof.h1@...pl>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> Cc: <stable@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  drivers/video/fbmem.c   |    3 ---
>  drivers/video/fbsysfs.c |    3 +++
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index 53ea056..1d8d098 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1513,9 +1513,6 @@ register_framebuffer(struct fb_info *fb_info)
>  		if (!registered_fb[i])
>  			break;
>  	fb_info->node = i;
> -	mutex_init(&fb_info->lock);
> -	mutex_init(&fb_info->mm_lock);
> -
>  	fb_info->dev = device_create(fb_class, fb_info->device,
>  				     MKDEV(FB_MAJOR, i), NULL, "fb%d", i);
>  	if (IS_ERR(fb_info->dev)) {
> diff --git a/drivers/video/fbsysfs.c b/drivers/video/fbsysfs.c
> index d4a2c11..60ddd1d 100644
> --- a/drivers/video/fbsysfs.c
> +++ b/drivers/video/fbsysfs.c
> @@ -58,6 +58,9 @@ struct fb_info *framebuffer_alloc(size_t size, struct device *dev)
>  
>  	info->device = dev;
>  
> +	mutex_init(&info->lock);
> +	mutex_init(&info->mm_lock);
> +
>  #ifdef CONFIG_FB_BACKLIGHT
>  	mutex_init(&info->bl_curve_mutex);
>  #endif

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