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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2015-10-20 11:38:08 -0400
committerSteven Rostedt <rostedt@goodmis.org>2015-10-20 11:38:08 -0400
commita2d7629048322ae62bff57f34f5f995e25ed234c (patch)
treeed52dce9e296f5d875b130162ef030dfa89d4f30 /kernel
parent7379047d5585187d1288486d4627873170d0005a (diff)
downloadlinux-a2d7629048322ae62bff57f34f5f995e25ed234c.tar.bz2
tracing: Have stack tracer force RCU to be watching
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: stable@vger.kernel.org # 4.2+ Cc: Peter Zijlstra <peterz@infradead.org> Cc:"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/trace_stack.c7
1 files changed, 7 insertions, 0 deletions
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);
}