On Thu, Oct 22, 2015 at 09:20:45AM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (Red Hat)" <[email protected]> > > The stack tracer was triggering the WARN_ON() in module.c: > > static void module_assert_mutex_or_preempt(void) > { > #ifdef CONFIG_LOCKDEP > if (unlikely(!debug_locks)) > return; > > WARN_ON(!rcu_read_lock_sched_held() && > !lockdep_is_held(&module_mutex)); > #endif > } > > The reason is that the stack tracer traces all function calls, and some of > those calls happen while exiting or entering user space and idle. Some of > these functions are called after RCU had already stopped watching, as RCU > does not watch userspace or idle CPUs. > > If a max stack is hit, then the save_stack_trace() is called, which will > check module addresses and call module_assert_mutex_or_preempt(), and then > trigger the warning. Sad part is, the warning itself will also do a stack > trace and tigger the same warning. That probably should be fixed. > > The warning was added by 0be964be0d45 "module: Sanitize RCU usage and > locking" but this bug has probably been around longer. But it's unlikely to > cause much harm, but the new warning causes the system to lock up. > > Cc: [email protected] # 4.2+ > Cc: Peter Zijlstra <[email protected]> > Cc:"Paul E. McKenney" <[email protected]> > Signed-off-by: Steven Rostedt <[email protected]>
It does look like it will make RCU pay attention in the region of interest. Acked-by: Paul E. McKenney <[email protected]> > --- > kernel/trace/trace_stack.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c > index b746399ab59c..5f29402bff0f 100644 > --- a/kernel/trace/trace_stack.c > +++ b/kernel/trace/trace_stack.c > @@ -88,6 +88,12 @@ check_stack(unsigned long ip, unsigned long *stack) > local_irq_save(flags); > arch_spin_lock(&max_stack_lock); > > + /* > + * RCU may not be watching, make it see us. > + * The stack trace code uses rcu_sched. > + */ > + rcu_irq_enter(); > + > /* In case another CPU set the tracer_frame on us */ > if (unlikely(!frame_size)) > this_size -= tracer_frame; > @@ -169,6 +175,7 @@ check_stack(unsigned long ip, unsigned long *stack) > } > > out: > + rcu_irq_exit(); > arch_spin_unlock(&max_stack_lock); > local_irq_restore(flags); > } > -- > 2.6.1 > > -- 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/
