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SubjectRe: [PATCH] fb: move mutex_init to framebuffer_alloc()
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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@linux-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@linux-sh.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Regards,
Wu Zhangjin

> Signed-off-by: Daniel Mack <daniel@caiaq.de>
> Cc:: Krzysztof Helt <krzysztof.h1@wp.pl>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Rafael J. Wysocki <rjw@sisk.pl>
> Cc: <stable@kernel.org>
> Cc: Andrew Morton <akpm@linux-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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