linux-kernel - Re: [BUG] drivers/video/sis: deadlock introduced by "fbdev: add mutex for fb

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Date:	Sun, 5 Jul 2009 18:43:19 +0200
From:	Krzysztof Helt <krzysztof.h1@...zta.fm>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Wu Zhangjin <wuzhangjin@...il.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mips@...ux-mips.org, Krzysztof Helt <krzysztof.h1@...pl>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ralf Baechle <ralf@...ux-mips.org>, ???? <yanh@...ote.com>,
	zhangfx <zhangfx@...ote.com>
Subject: Re: [BUG] drivers/video/sis: deadlock introduced by
 "fbdev: add mutex for fb_mmap locking"

On Mon, 6 Jul 2009 00:25:57 +0900
Paul Mundt <lethal@...ux-sh.org> wrote:

> Ok, here is an updated version with an updated matroxfb and the sm501fb
> change reverted.
> 
> Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
> 

Here is a patch which should fix problem with sm501fb driver:

diff --git a/drivers/video/sm501fb.c b/drivers/video/sm501fb.c
index 16d4f4c..924d794 100644
--- a/drivers/video/sm501fb.c
+++ b/drivers/video/sm501fb.c
@@ -1540,9 +1540,6 @@ static int sm501fb_init_fb(struct fb_info *fb,
 	if (ret)
 		dev_err(info->dev, "check_var() failed on initial setup?\n");
 
-	/* ensure we've activated our new configuration */
-	(fb->fbops->fb_set_par)(fb);
-
 	return 0;
 }
 

Paul, please test it (without additional initialization of the mm_lock mutext). I will post the patch
if it works for you.

An issue here is that these drivers calls fb_set_par() function (or part of it as the sisfb driver) 
but the register_framebuffer() calls the fb_set_par() also after all structures are set up. There
should be no need to call the fb_set_par() just before the register_framebuffer().

The matroxfb driver is quite far from standard driver framework by now. I vote for fixing it
by adding this early initialization of the mm_mutex for now.

Kind regards,
Krzysztof

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