Messages in this thread | | | Date | Tue, 20 Oct 2015 18:39:52 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] module: Prevent recursion bug caused by module RCU check |
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On Tue, Oct 20, 2015 at 12:21:03PM -0400, Steven Rostedt wrote: > +++ b/kernel/module.c > @@ -284,11 +284,25 @@ static void module_assert_mutex(void) > static void module_assert_mutex_or_preempt(void) > { > #ifdef CONFIG_LOCKDEP > + static int once; > + > if (unlikely(!debug_locks)) > return; > > - WARN_ON(!rcu_read_lock_sched_held() && > - !lockdep_is_held(&module_mutex)); > + /* > + * Would be nice to use WARN_ON_ONCE(), but the warning > + * that causes a stack trace may call __module_address() > + * which may call here, and we trigger the warning again, > + * before the WARN_ON_ONCE() updates its flag. > + * To prevent the recursion, we need to open code the > + * once logic. > + */ > + if (!once && > + unlikely(!rcu_read_lock_sched_held() && > + !lockdep_is_held(&module_mutex))) { > + once++;
once = 1;
is more 'once' :-) Otherwise its once every 4-odd billion.
> + WARN_ON(1); > + } > #endif > } >
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