[PATCH] lockdep: call time_hardirqs_off after clearing hardirqs_enabled

From: Qi Hou
Date: Mon Mar 13 2017 - 22:01:16 EST


The current order of calls within trace_hardirqs_off_caller() 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()
|- time_hardirqs_off()
|- trace_preemptirqsoff_hist_rcuidle()
|- __DO_TRACE()
|- rcu_dereference_sched()
|- rcu_read_lock_sched_held()
|- lock_is_held()
|- check_flags()

The order of calls within trace_hardirqs_off_caller() simplified as below:

local_irq_disable()
|- raw_local_irq_disable()
|- trace_hardirqs_off()
|- trace_hardirqs_off_caller()
|- time_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 time_hardirqs_off()
after that we clear hardirqs_enabled.

Signed-off-by: Qi Hou <qi.hou@xxxxxxxxxxxxx>
---
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