linux-kernel - Re: [PATCH] lockdep: call trace_hardirqs_off after clearing hardirqs

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Date:   Mon, 13 Mar 2017 10:05:21 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Qi Hou <qi.hou@...driver.com>
Cc:     <mingo@...hat.com>, <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, <C.Emde@...dl.org>,
        <paul.gortmaker@...driver.com>, <bruce.ashfield@...driver.com>
Subject: Re: [PATCH] lockdep: call trace_hardirqs_off after clearing
 hardirqs_enabled

On Mon, 13 Mar 2017 18:08:48 +0800
Qi Hou <qi.hou@...driver.com> 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:
> 
> local_irq_disable()
>  |- trace_hardirqs_off()
>      |- trace_hardirqs_off_caller()
>          |- preemptirqsoff_hist()

There is no preemptirqsoff_hist() function in the kernel.

-- 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:
> 
> 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@...driver.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);
>