Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

[Andrew Morton]

On Thu, 21 Sep 2006 14:19:52 +0200
Olaf Hering <olaf@aepfle.de> wrote:

> The bl_curve code has some room for improvement.
> 
> ...
> <6>Monitor sense value = 0x60b
> <6>using video mode 13 and color mode 0.
> <4>Console: switching to colour frame buffer device 104x39
> <6>fb0: valkyrie frame buffer device
> ...
> 
> inst-sys:~ # cat /proc/fb
> 0 valkyrie
> inst-sys:~ # l /sys/class/graphics/fb0/
> total 0
> drwxr-xr-x 2 root root    0 Sep 21 11:54 ./
> drwxr-xr-x 4 root root    0 Sep 21 11:53 ../
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 bits_per_pixel
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 bl_curve
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 blank
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 console
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 cursor
> -r--r--r-- 1 root root 4096 Sep 21 12:15 dev
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 mode
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 modes
> -r--r--r-- 1 root root 4096 Sep 21 12:15 name
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 pan
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 rotate
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 state
> -r--r--r-- 1 root root 4096 Sep 21 12:15 stride
> lrwxrwxrwx 1 root root    0 Sep 21 12:15 subsystem -> ../../../class/graphics/
> --w------- 1 root root 4096 Sep 21 12:15 uevent
> -rw-r--r-- 1 root root 4096 Sep 21 12:15 virtual_size
> inst-sys:~ # head /sys/class/graphics/fb0/*
> ==> /sys/class/graphics/fb0/bits_per_pixel <==
> 8
> 
> ==> /sys/class/graphics/fb0/bl_curve <==
> Segmentation fault
> inst-sys:~ # dmesg
> valkyriefb: vmode 13 does not support cmode 1.
> Unable to handle kernel paging request for data at address 0x00000000
> Faulting instruction address: 0xc02c7bd8
> Oops: Kernel access of bad area, sig: 11 [#1]
> 
> Modules linked in: tulip mesh cpufreq_ondemand loop nfs nfs_acl lockd sunrpc sg st sd_mod sr_mod scsi_mod ide_cd cdrom
> NIP: C02C7BD8 LR: C0170EBC CTR: C0170E90
> REGS: c4209db0 TRAP: 0300   Not tainted  (2.6.18-rc7-git1-2-default)
> MSR: 00009032 <EE,ME,IR,DR>  CR: 28042488  XER: 00000000
> DAR: 00000000, DSISR: 22000000
> TASK = c7fc8190[2853] 'head' THREAD: c4208000
> GPR00: C4209E6C C4209E60 C7FC8190 C0B77614 C41D5000 C41D5000 00000000 00008000
> GPR08: 00000000 C0B77618 00000000 00000000 00000000 100200C8 10020000 00000001
> GPR16: 10006D08 7FDF9B3C 100A0000 10080000 00000003 7FDF9CAB C4209F20 C2FCDC78
> GPR24: C038BC14 C01EF568 7FDF7858 C41D5000 C0B77614 C0B77400 C7FC8190 C0B77614
> NIP [C02C7BD8] __mutex_lock_slowpath+0x2c/0xa4
> LR [C0170EBC] show_bl_curve+0x2c/0xa0
> Call Trace:  
> [C4209E60] [C02C7A54] mutex_lock+0x18/0x5c (unreliable)
> [C4209E80] [C0170EBC] show_bl_curve+0x2c/0xa0
> [C4209EB0] [C01EF594] class_device_attr_show+0x2c/0x44
> [C4209EC0] [C00CC3BC] sysfs_read_file+0xb8/0x204
> [C4209EF0] [C0083FE4] vfs_read+0xec/0x1c8
> [C4209F10] [C0084444] sys_read+0x4c/0x8c
> [C4209F40] [C00125F8] ret_from_syscall+0x0/0x40
> --- Exception: c01 at 0xff589f8
>     LR = 0x100045e0
> Instruction dump:
> 4e800020 9421ffe0 7c0802a6 39230004 bfc10018 7c7f1b78 7c5e1378 90010024
> 3801000c 9121000c 81690004 90090004 <900b0000> 91610010 90410014 3800ffff
> 

cc's added.


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Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

[Michael Hanselmann]

On Thu, Sep 21, 2006 at 12:37:42PM -0700, Andrew Morton wrote:
> On Thu, 21 Sep 2006 14:19:52 +0200
> Olaf Hering <olaf@aepfle.de> wrote:
> > The bl_curve code has some room for improvement.

Agreed.

> > inst-sys:~ # dmesg
> > valkyriefb: vmode 13 does not support cmode 1.
> > Unable to handle kernel paging request for data at address 0x00000000
> > Faulting instruction address: 0xc02c7bd8

Seems like not all drivers use the framebuffer_alloc() function and
won't have an initialized mutex. But those don't have a backlight,
anyway.

What about the patch below? Does it work for you?

Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>

---
diff -Nrup --exclude-from linux-exclude-from linux-2.6.18.orig/drivers/video/fbsysfs.c linux-2.6.18/drivers/video/fbsysfs.c
--- linux-2.6.18.orig/drivers/video/fbsysfs.c	2006-09-21 23:40:06.000000000 +0200
+++ linux-2.6.18/drivers/video/fbsysfs.c	2006-09-21 23:50:00.000000000 +0200
@@ -397,6 +397,12 @@ static ssize_t store_bl_curve(struct cla
 	u8 tmp_curve[FB_BACKLIGHT_LEVELS];
 	unsigned int i;
 
+	/* Some drivers don't use framebuffer_alloc(), but those also
+	 * don't have backlights.
+	 */
+	if (!fb_info || !fb_info->bl_dev)
+		return -ENODEV;
+
 	if (count != (FB_BACKLIGHT_LEVELS / 8 * 24))
 		return -EINVAL;
 
@@ -430,6 +436,12 @@ static ssize_t show_bl_curve(struct clas
 	ssize_t len = 0;
 	unsigned int i;
 
+	/* Some drivers don't use framebuffer_alloc(), but those also
+	 * don't have backlights.
+	 */
+	if (!fb_info || !fb_info->bl_dev)
+		return -ENODEV;
+
 	mutex_lock(&fb_info->bl_mutex);
 	for (i = 0; i < FB_BACKLIGHT_LEVELS; i += 8)
 		len += snprintf(&buf[len], PAGE_SIZE,

Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

[Olaf Hering]

On Thu, Sep 21, Michael Hanselmann wrote:

> What about the patch below? Does it work for you?

Appears to work.

tangerine:~ # head /sys/class/graphics/fb0/*
==> /sys/class/graphics/fb0/bits_per_pixel <==
8

==> /sys/class/graphics/fb0/bl_curve <==
head: error reading `/sys/class/graphics/fb0/bl_curve': No such device

==> /sys/class/graphics/fb0/blank <==

==> /sys/class/graphics/fb0/console <==

==> /sys/class/graphics/fb0/cursor <==

==> /sys/class/graphics/fb0/dev <==
29:0

==> /sys/class/graphics/fb0/mode <==

==> /sys/class/graphics/fb0/modes <==
U:832x624p-74

==> /sys/class/graphics/fb0/name <==
valkyrie

==> /sys/class/graphics/fb0/pan <==
0,0

==> /sys/class/graphics/fb0/rotate <==
0

==> /sys/class/graphics/fb0/state <==
0

==> /sys/class/graphics/fb0/stride <==
832

==> /sys/class/graphics/fb0/subsystem <==
head: error reading `/sys/class/graphics/fb0/subsystem': Is a directory
head: cannot open `/sys/class/graphics/fb0/uevent' for reading: Permission denied

==> /sys/class/graphics/fb0/virtual_size <==
832,624

Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

[Andrew Morton]

On Fri, 22 Sep 2006 13:26:22 +0200
Olaf Hering <olaf@aepfle.de> wrote:

> On Thu, Sep 21, Michael Hanselmann wrote:
> 
> > What about the patch below? Does it work for you?
> 
> Appears to work.
> 
> tangerine:~ # head /sys/class/graphics/fb0/*
> ==> /sys/class/graphics/fb0/bits_per_pixel <==
> 8
> 
> ==> /sys/class/graphics/fb0/bl_curve <==
> head: error reading `/sys/class/graphics/fb0/bl_curve': No such device
> 
> ==> /sys/class/graphics/fb0/blank <==
> 
> ==> /sys/class/graphics/fb0/console <==
> 
> ==> /sys/class/graphics/fb0/cursor <==
> 
> ==> /sys/class/graphics/fb0/dev <==
> 29:0
> 
> ==> /sys/class/graphics/fb0/mode <==
> 
> ==> /sys/class/graphics/fb0/modes <==
> U:832x624p-74
> 
> ==> /sys/class/graphics/fb0/name <==
> valkyrie
> 
> ==> /sys/class/graphics/fb0/pan <==
> 0,0
> 
> ==> /sys/class/graphics/fb0/rotate <==
> 0
> 
> ==> /sys/class/graphics/fb0/state <==
> 0
> 
> ==> /sys/class/graphics/fb0/stride <==
> 832
> 
> ==> /sys/class/graphics/fb0/subsystem <==
> head: error reading `/sys/class/graphics/fb0/subsystem': Is a directory
> head: cannot open `/sys/class/graphics/fb0/uevent' for reading: Permission denied
> 
> ==> /sys/class/graphics/fb0/virtual_size <==
> 832,624

Still looks like a bit of a mess, but I assume that's expected.

Michael, I take it that patch was final?

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Re: backlight: oops in __mutex_lock_slowpath during head /sys/class/graphics/fb0/* in 2.6.18

[Michael Hanselmann]

On Fri, Sep 22, 2006 at 04:02:55PM -0700, Andrew Morton wrote:
> Still looks like a bit of a mess, but I assume that's expected.

> Michael, I take it that patch was final?

For now, yes. Thanks for adding it to -mm.