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

[qhou]

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:
> >
> > local_irq_disable()
> >   |- 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
kernel/locking/lockdep.c.

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:
> >
> > 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@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);
> >   

--
Best regards,
Qi Hou
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