Date: Fri, 10 Aug 2007 00:55:17 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Mariusz Kozlowski <m.kozlowski@tuxland.pl>, josh@freedesktop.org,
       linux-kernel@vger.kernel.org, "Randy.Dunlap" <rdunlap@xenotime.net>
Subject: Re: 2.6.23-rc2-mm1: sleeping function called from invalid context
 at kernel/mutex.c:86
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On Fri, 10 Aug 2007 09:40:00 +0200 Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > We seem to have made a mess in there.  timer_list_show() ends up 
> > calling lookup_module_symbol_name(), which takes a mutex.  However 
> > print_symbol() (which is called at oops time, interrupt time, etc) 
> > calls module_address_lookup(), which is basically the same, only it 
> > doesn't take the mutex.
> 
> hm, current upstream does:
> 
>  static void print_name_offset(struct seq_file *m, void *sym)
>  {
>          char symname[KSYM_NAME_LEN];
> 
>          if (lookup_symbol_name((unsigned long)sym, symname) < 0)
> 
> why was that changed?

It wasn't.  lookup_symbol_name() calls lookup_module_symbol_name() which
calls mutex_lock().

> I think symbol lookups for debug purposes have to 
> be lockless, fundamentally.
> 

Sure, especially a sysrq thingy.

It's a bit nasty to just go in there and start walking data structures
without holding the needed lock though.

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