Massive log spam loading modules on ARM after 3.2-rc5 (regression)

[Uwe Kleine-König]

On Wed, Dec 14, 2011 at 04:51:33PM -0500, Nick Bowler wrote:
> Hi folks,
> 
> With latest Linus' master, I'm faced with massive log spam on our ARM
> Versatile Express platform when using modules.  Here's an example:
> 
>   # modprobe sp805-wdt
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   sp805-wdt mb:wdt: registration successful
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
>   unwind: Unknown symbol address 7f802009
>   unwind: Index not found 7f802009
> 
> The message only seem to get printed at module load time.  Other than
> the noise, things _seem_ to be working.  Nevertheless, it's a regression
> introduced after 3.2-rc5 by the following commit:
> 
>   de66a979012dbc66b1ec0125795a3f79ee667b8a is the first bad commit
>   commit de66a979012dbc66b1ec0125795a3f79ee667b8a
>   Author: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
>   Date:   Mon Dec 5 09:39:59 2011 +0100
> 
>       ARM: 7187/1: fix unwinding for XIP kernels
> 
>       The linker places the unwind tables in readonly sections. So when using
>       an XIP kernel these are located in ROM and cannot be modified.
>       For that reason the current approach to convert the relative offsets in
>       the unwind index to absolute addresses early in the boot process doesn't
>       work with XIP.
> 
>       The offsets in the unwind index section are signed 31 bit numbers and
>       the structs are sorted by this offset. So it first has offsets between
>       0x40000000 and 0x7fffffff (i.e. the negative offsets) and then offsets
>       between 0x00000000 and 0x3fffffff. When seperating these two blocks the
>       numbers are sorted even when interpreting the offsets as unsigned longs.
> 
>       So determine the first non-negative entry once and track that using the
>       new origin pointer. The actual bisection can then use a plain unsigned
>       long comparison. The only thing that makes the new bisection more
>       complicated is that the offsets are relative to their position in the
>       index section, so the key to search needs to be adapted accordingly in
>       each step.
> 
>       Moreover several consts are added to catch future writes and rename the
>       member "addr" of struct unwind_idx to "addr_offset" to better match the
>       new semantic. (This has the additional benefit of breaking eventual
>       users at compile time to make them aware of the change.)
> 
>       In my tests the new algorithm was a tad faster than the original and has
>       the additional upside of not needing the initial conversion and so saves
>       some boot time and it's possible to unwind even earlier.
> 
>       Acked-by: Catalin Marinas <catalin.marinas at arm.com>
>       Acked-by: Nicolas Pitre <nico at fluxnic.net>
>       Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
>       Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> 
>   :040000 040000 9c4363228515808d71dac84a4a16e0aa0cf4ceaa 65b80d4e51fabf0a3142a880be795f4b38f4d9fe M	arch
> 
> I am *not* using XIP.  Reverting this commit resolves the issue.
I'd say revert that change for now, I'll take a look. (IMHO this is
merge window material even though it has "fix" in the title. The
addressed problem is only relevant on XIP (which isn't used much AFAIK)
and is broken since 2.6.30-rc1~636^2~52^2~18 when unwinding was
introduced.)

> Let me know if you need any more info,
I know where to look, I'll address you via private mail if I need some
more data.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |