Re: [PATCH] lockdep: call trace_hardirqs_off after clearing hardirqs_enabled

From: qhou
Date: Mon Mar 13 2017 - 21:25:05 EST

On 2017å03æ13æ 22:05, Steven Rostedt wrote:
On Mon, 13 Mar 2017 18:08:48 +0800
Qi Hou <qi.hou@xxxxxxxxxxxxx> wrote:

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:

|- trace_hardirqs_off()
|- trace_hardirqs_off_caller()
|- preemptirqsoff_hist()
There is no preemptirqsoff_hist() function in the kernel.
Sorry, it's a mistake. It should have been "trace_hardirqs_off_caller()", defined in file

And it will call trace_preemptirqsoff_hist_rcuidle(), trace_preemptirqsoff_hist_rcuidle will()
call check_flags().

I will correct it. And after carefully checking the patch, I will re-send it.

Very very sorry for my mistake. That wasted your time.

Best regards,
Qi Hou

-- Steve

|- __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:

|- 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@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))
@@ -2649,6 +2647,8 @@ __visible void trace_hardirqs_off_caller(unsigned long ip)
} else
+ time_hardirqs_off(CALLER_ADDR0, ip);

Best regards,
Qi Hou
Phone number: +86-10-8477-8608
Address: Floor 15, Building B, Wangjing Plaza, No.9 Zhong-Huan Nanlu, Chaoyang District