Messages in this thread | | | Date | Sat, 11 Aug 2007 11:24:22 +0400 | From | Alexey Dobriyan <> | Subject | Re: 2.6.23-rc2-mm1: sleeping function called from invalid context at kernel/mutex.c:86 |
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On Fri, Aug 10, 2007 at 12:55:17AM -0700, Andrew Morton wrote: > 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.
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.
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