Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

[Andrew James Wade <andrew.j.wade@gmail.com>]

On Thursday 05 October 2006 04:36, Andrew Morton wrote:
> On Thu, 5 Oct 2006 04:13:07 -0400
> Andrew James Wade <andrew.j.wade@gmail.com> wrote:
> 
> > (...)
> 
> 
> That all looks OK (by sheer luck).
> 
> Well.  What's the cache line size on that machine?  Every exit() will cause
> a down_read() on task_exit_notifier's lock which might affect things.  And
> I think you snipped the above list a bit short (depending on that line
> size).
> 
> 
> But still, we know that moving those things into __read_mostly didn't fix
> it, yes?

No. To my knowledge Tim Chen hasn't tried __read_mostly, and I have not
attempted to replicate the test case. (I only have a uniprocessor
machine.) Core 2 machines have a cache line size of 64 bytes, but Tim
Chen is likely using a different kernel/.config than I am so my objdump
isn't definitive.

Tim, perhaps you can try the __read_mostly marking as Andrew suggests?

signed-off-by: Andrew Wade <andrew.j.wade@gmail.com>
upN a/include/asm-generic/bug.h b/include/asm-generic/bug.h
--- a/include/asm-generic/bug.h	2006-10-05 16:16:37.000000000 -0400
+++ b/include/asm-generic/bug.h	2006-10-05 16:33:08.000000000 -0400
@@ -42,7 +42,7 @@
 #endif
 
 #define WARN_ON_ONCE(condition)	({			\
-	static int __warn_once = 1;			\
+	static int __warn_once __read_mostly = 1;	\
 	typeof(condition) __ret_warn_once = (condition);\
 							\
 	if (likely(__warn_once))			\
-
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