Re: 2.6.23-rc2-mm1: sleeping function called from invalid context at kernel/mutex.c:86

Andrew Morton
2007-08-10T07:55:53Z

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.