On Fri, Aug 10, 2007 at 12:55:17AM -0700, Andrew Morton wrote: > On Fri, 10 Aug 2007 09:40:00 +0200 Ingo Molnar <[EMAIL PROTECTED]> wrote: > > > > > * Andrew Morton <[EMAIL PROTECTED]> 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.
Oh no, it was! commit 9d65cb4a1718a072898c7a57a3bc61b2dc4bcd4d Fix race between cat /proc/*/wchan and rmmod et al kallsyms_lookup() can go iterating over modules list unprotected which is OK for emergency situations (oops), but not OK for regular stuff like /proc/*/wchan. > 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. I imagine user running powertop which IIRC trolls /proc/timer_list and doing rmmod following powertop instructions. > It's a bit nasty to just go in there and start walking data structures > without holding the needed lock though. Yep. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/