[PATCH] lockdep: call trace_hardirqs_off after clearing hardirqs_enabled

* [PATCH] lockdep: call trace_hardirqs_off after clearing hardirqs_enabled
@ 2017-03-13 10:08 Qi Hou
  2017-03-13 14:05 ` Steven Rostedt
  2017-03-13 14:37 ` Peter Zijlstra
  0 siblings, 2 replies; 4+ messages in thread
From: Qi Hou @ 2017-03-13 10:08 UTC (permalink / raw)
  To: mingo, rostedt, tglx; +Cc: linux-kernel, C.Emde, paul.gortmaker, bruce.ashfield

The current order of calls within trace_hardirqs_off() would provoke an
"unannotated irqs-off" WARNING.

This warning was reported by check_flags() when it found that the hardirqs has
been disabled but the irq-flags state, hardirqs_enabled, has not been cleared.

Check_flags() is called via trace_hardirqs_off(), and trace_hardirqs_off() will
be called by functions kind of local_irq_disable() if CONFIG_TRACE_IRQFLAGS has
been enabled.

The calltrace from functions kind of local_irq_diasble() to check_flags()
simplied as below:

local_irq_disable()
 |- trace_hardirqs_off()
     |- trace_hardirqs_off_caller()
         |- preemptirqsoff_hist()
            |- __DO_TRACE()
               |- rcu_dereference_sched()
                   |- rcu_read_lock_sched_held()
                       |- lock_is_held()
                           |- check_flags()

The order of calls within trace_hardirqs_off() can be simplified as below:

local_irq_disable()
 |- raw_local_irq_disable()
 |- trace_hardirqs_off()
     |- trace_hardirqs_off() --> check_flags()
     |- hardirqs_enabled = 0

We could find that the call to check_flags() has been made between disabling
hardirqs and clearing hardirqs_enabled. That will definitely cause an
"unannotated irqs-off" warning.

To fix this "unannotated irqs-off" warning, we must call trace_hardirqs_off()
after that we clear hardirqs_enabled.

Signed-off-by: Qi Hou <qi.hou@windriver.com>
---
 kernel/locking/lockdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 577f026..e8b35e4 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2627,8 +2627,6 @@ __visible void trace_hardirqs_off_caller(unsigned long ip)
 {
 	struct task_struct *curr = current;
 
-	time_hardirqs_off(CALLER_ADDR0, ip);
-
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
 
@@ -2649,6 +2647,8 @@ __visible void trace_hardirqs_off_caller(unsigned long ip)
 		debug_atomic_inc(hardirqs_off_events);
 	} else
 		debug_atomic_inc(redundant_hardirqs_off);
+
+	time_hardirqs_off(CALLER_ADDR0, ip);
 }
 EXPORT_SYMBOL(trace_hardirqs_off_caller);
 
-- 
1.9.1

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