diff mbox

[BUG] drivers/video/sis: deadlock introduced by "fbdev: add mutex for fb_mmap locking"

Message ID 20090705181808.93be24a9.krzysztof.h1@poczta.fm (mailing list archive)
State Not Applicable
Headers show

Commit Message

Krzysztof Helt July 5, 2009, 4:18 p.m. UTC 
On Mon, 6 Jul 2009 00:25:57 +0900
Paul Mundt <lethal@linux-sh.org> wrote:

> On Sun, Jul 05, 2009 at 08:19:40AM -0700, Linus Torvalds wrote:
> > 
> > 
> > On Mon, 6 Jul 2009, Paul Mundt wrote:
> > > >
> > > > Why not "lock" as well?
> > > 
> > > I had that initially, but matroxfb will break if we do that, and
> > > presently nothing cares about trying to take ->lock that early on.
> > 
> > I really would rather have consistency than some odd rules like that.
> > 
> > In particular - if matroxfb is different and needs its own lock 
> > initialization because it doesn't use the common allocation routine, then 
> > please make _that_ consistent too. Rather than have it special-case just 
> > one lock that it needs to initialize separately, make it clear that since 
> > it does its own allocations it needs to initialize _everything_ 
> > separately.
> > 
> Ok, here is an updated version with an updated matroxfb and the sm501fb
> change reverted.
> 
> Signed-off-by: Paul Mundt <lethal@linux-sh.org>
> 
> ---
> 

This is incorrect way to fix this as some drivers do not use the framebuffer_alloc() 
at all. They use global (for a file) fb_info structure. I have done some cleanups to
the fbdev layer before the 2.6.31 and there should no drivers which uses kmalloc or
kzalloc to allocate the fb_info (your patch would break these drivers too).

A root of the whole mm_lock issue is that the fb_mmap() BKL protected two fb_info
fields which were never protected when set. I changed this by add the mm_lock 
around these fields but only in drivers which modified this fields AFTER call
to the register_framebuffer(). Some drivers set these fields using the same
function before and after the register_framebuffer(). I strongly believe that
setting these fields before the register_framebuffer() is wrong or redundant for
these drivers. See my fix for the sisfb driver below. 

I have tested the patch below. Wu Zhangjin, can you also confirm that this 
works for you (without your patch)?

I will look into the matroxfb and sm501fb drivers now. The same problem is
already fixed for the mx3fb driver and the patch is sent to Andrew Morton.

Regards,
Krzysztof


From: Krzysztof Helt <krzysztof.h1@wp.pl>

Remove redundant call to the sisfb_get_fix() before sis frambuffer is registered.

This fixes a problem with uninitialized the fb_info->mm_lock mutex.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
---




----------------------------------------------------------------------
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http://link.interia.pl/f222

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Comments

Wu Zhangjin July 6, 2009, 1:13 a.m. UTC | #1 
Hi,

On Sun, 2009-07-05 at 18:18 +0200, Krzysztof Helt wrote:
> On Mon, 6 Jul 2009 00:25:57 +0900
> Paul Mundt <lethal@linux-sh.org> wrote:
> 
> > On Sun, Jul 05, 2009 at 08:19:40AM -0700, Linus Torvalds wrote:
> > > 
> > > 
> > > On Mon, 6 Jul 2009, Paul Mundt wrote:
> > > > >
> > > > > Why not "lock" as well?
> > > > 
> > > > I had that initially, but matroxfb will break if we do that, and
> > > > presently nothing cares about trying to take ->lock that early on.
> > > 
> > > I really would rather have consistency than some odd rules like that.
> > > 
> > > In particular - if matroxfb is different and needs its own lock 
> > > initialization because it doesn't use the common allocation routine, then 
> > > please make _that_ consistent too. Rather than have it special-case just 
> > > one lock that it needs to initialize separately, make it clear that since 
> > > it does its own allocations it needs to initialize _everything_ 
> > > separately.
> > > 
> > Ok, here is an updated version with an updated matroxfb and the sm501fb
> > change reverted.
> > 
> > Signed-off-by: Paul Mundt <lethal@linux-sh.org>
> > 
> > ---
> > 
> 
> This is incorrect way to fix this as some drivers do not use the framebuffer_alloc() 
> at all. They use global (for a file) fb_info structure. I have done some cleanups to
> the fbdev layer before the 2.6.31 and there should no drivers which uses kmalloc or
> kzalloc to allocate the fb_info (your patch would break these drivers too).
> 
> A root of the whole mm_lock issue is that the fb_mmap() BKL protected two fb_info
> fields which were never protected when set. I changed this by add the mm_lock 
> around these fields but only in drivers which modified this fields AFTER call
> to the register_framebuffer(). Some drivers set these fields using the same
> function before and after the register_framebuffer(). I strongly believe that
> setting these fields before the register_framebuffer() is wrong or redundant for
> these drivers. See my fix for the sisfb driver below. 
> 
> I have tested the patch below. Wu Zhangjin, can you also confirm that this 
> works for you (without your patch)?
> 

This patch also works for me, thanks!

Regards,
Wu Zhangjin

> I will look into the matroxfb and sm501fb drivers now. The same problem is
> already fixed for the mx3fb driver and the patch is sent to Andrew Morton.
> 
> Regards,
> Krzysztof
> 
> 
> From: Krzysztof Helt <krzysztof.h1@wp.pl>
> 
> Remove redundant call to the sisfb_get_fix() before sis frambuffer is registered.
> 
> This fixes a problem with uninitialized the fb_info->mm_lock mutex.
> 
> Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
> ---
> 
> diff -urp linux-ref/drivers/video/sis/sis_main.c linux-next/drivers/video/sis/sis_main.c
> --- linux-ref/drivers/video/sis/sis_main.c	2009-07-01 18:07:05.000000000 +0200
> +++ linux-next/drivers/video/sis/sis_main.c	2009-07-05 17:20:33.000000000 +0200
> @@ -6367,7 +6367,6 @@ error_3:	vfree(ivideo->bios_abase);
>  		sis_fb_info->fix = ivideo->sisfb_fix;
>  		sis_fb_info->screen_base = ivideo->video_vbase + ivideo->video_offset;
>  		sis_fb_info->fbops = &sisfb_ops;
> -		sisfb_get_fix(&sis_fb_info->fix, -1, sis_fb_info);
>  		sis_fb_info->pseudo_palette = ivideo->pseudo_palette;
>  
>  		fb_alloc_cmap(&sis_fb_info->cmap, 256 , 0);
> 
> 
> 
> ----------------------------------------------------------------------
> Najlepsze OC i AC tylko w Ergo Hestia
> http://link.interia.pl/f222
> 

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Krzysztof Helt July 6, 2009, 2:50 p.m. UTC | #2 
On Mon, 06 Jul 2009 09:13:11 +0800
Wu Zhangjin <wuzhangjin@gmail.com> wrote:

> Hi,
> 
> 
> This patch also works for me, thanks!
> 
> Regards,
> Wu Zhangjin
> 

Who should I send this patch to be included as a 2.6.31 regression fix?

Regards,
Krzysztof

> > 
> > From: Krzysztof Helt <krzysztof.h1@wp.pl>
> > 
> > Remove redundant call to the sisfb_get_fix() before sis frambuffer is registered.
> > 
> > This fixes a problem with uninitialized the fb_info->mm_lock mutex.
> > 
> > Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
> > ---
> > 
> > diff -urp linux-ref/drivers/video/sis/sis_main.c linux-next/drivers/video/sis/sis_main.c
> > --- linux-ref/drivers/video/sis/sis_main.c	2009-07-01 18:07:05.000000000 +0200
> > +++ linux-next/drivers/video/sis/sis_main.c	2009-07-05 17:20:33.000000000 +0200
> > @@ -6367,7 +6367,6 @@ error_3:	vfree(ivideo->bios_abase);
> >  		sis_fb_info->fix = ivideo->sisfb_fix;
> >  		sis_fb_info->screen_base = ivideo->video_vbase + ivideo->video_offset;
> >  		sis_fb_info->fbops = &sisfb_ops;
> > -		sisfb_get_fix(&sis_fb_info->fix, -1, sis_fb_info);
> >  		sis_fb_info->pseudo_palette = ivideo->pseudo_palette;
> >  
> >  		fb_alloc_cmap(&sis_fb_info->cmap, 256 , 0);
> > 
> > 
> > 
> > ----------------------------------------------------------------------
> > Najlepsze OC i AC tylko w Ergo Hestia
> > http://link.interia.pl/f222
> > 
> 
> 

----------------------------------------------------------------------
Najlepsze OC i AC tylko w Ergo Hestia
http://link.interia.pl/f222

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Linus Torvalds July 6, 2009, 4:29 p.m. UTC | #3 
On Mon, 6 Jul 2009, Krzysztof Helt wrote:
> 
> Who should I send this patch to be included as a 2.6.31 regression fix?

Just send the patches to me. I've got the patch, but no changelog, and so 
I'd like to see them again, with changelogs and the proper "Acked-by:" or 
"Tested-by" lines etc.

		Linus
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diff mbox

Patch

diff -urp linux-ref/drivers/video/sis/sis_main.c linux-next/drivers/video/sis/sis_main.c
--- linux-ref/drivers/video/sis/sis_main.c	2009-07-01 18:07:05.000000000 +0200
+++ linux-next/drivers/video/sis/sis_main.c	2009-07-05 17:20:33.000000000 +0200
@@ -6367,7 +6367,6 @@  error_3:	vfree(ivideo->bios_abase);
 		sis_fb_info->fix = ivideo->sisfb_fix;
 		sis_fb_info->screen_base = ivideo->video_vbase + ivideo->video_offset;
 		sis_fb_info->fbops = &sisfb_ops;
-		sisfb_get_fix(&sis_fb_info->fix, -1, sis_fb_info);
 		sis_fb_info->pseudo_palette = ivideo->pseudo_palette;
 
 		fb_alloc_cmap(&sis_fb_info->cmap, 256 , 0);