Re: [PATCH] Fix WARN_ON / WARN_ON_ONCE regression

Andrew Morton
2006-10-05T08:40:04Z

On Thu, 5 Oct 2006 04:13:07 -0400
Andrew James Wade <andrew.j.wade@gmail.com> wrote:

> (from earlier)
> > Perhaps the `static int __warn_once' is getting put in the same cacheline
> > as some frequently-modified thing.
>
> hmm:
>
> 00000460 l O .data 00000044 task_exit_notifier
> 000004c0 l O .data 0000002c task_free_notifier
> 000004ec l O .data 00000004 warnlimit.15904
> 000004f0 l O .data 00000004 firsttime.15774
> 000004f4 l O .data 00000004 __warn_once.15180
> 000004f8 l O .data 00000004 __warn_once.15174
> 000004fc l O .data 00000004 __warn_once.15213
> 00000500 l O .data 00000004 __warn_once.15207
> 00000504 l O .data 00000004 __warn_once.15145
> 00000508 l O .data 00000004 __warn_once.15309
> 0000050c l O .data 00000004 __warn_once.15256
> 00000510 l O .data 00000004 __warn_once.15250
> 000005a0 l O .data 0000006c proc_iomem_operations
> (extracted from objdump -t kernel/built-in.o)

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?