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

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Date:   Mon, 13 Mar 2017 23:03:54 -0400
From:   Paul Gortmaker <paul.gortmaker@...il.com>
To:     Qi Hou <qi.hou@...driver.com>
Cc:     Ingo Molnar <mingo@...hat.com>, rostedt@...dmis.org,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, C.Emde@...dl.org,
        "bruce.ashfield" <bruce.ashfield@...driver.com>
Subject: Re: [PATCH] lockdep: call time_hardirqs_off after clearing hardirqs_enabled

Please stop sending "guesswork" patches.  This message to you is not
new.   I am running out of avenues where I can ask you to cease and
desist;  spamming maintainers like this is not acceptable.  You are
one step away from being in a kill-file.

On Mon, Mar 13, 2017 at 10:00 PM, Qi Hou <qi.hou@...driver.com> wrote:
> 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@...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);
>
> --
> 1.9.1
>