linux-kernel - Re: [tip: locking/core] lockdep: Add hrtimer context tracing bits

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Date:   Sat, 21 Mar 2020 17:46:43 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>
Subject: Re: [tip: locking/core] lockdep: Add hrtimer context tracing bits

On Sat, Mar 21, 2020 at 03:53:45PM -0000, tip-bot2 for Sebastian Andrzej Siewior wrote:
> The following commit has been merged into the locking/core branch of tip:
> 
> Commit-ID:     40db173965c05a1d803451240ed41707d5bd978d
> Gitweb:        https://git.kernel.org/tip/40db173965c05a1d803451240ed41707d5bd978d
> Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> AuthorDate:    Sat, 21 Mar 2020 12:26:02 +01:00
> Committer:     Peter Zijlstra <peterz@...radead.org>
> CommitterDate: Sat, 21 Mar 2020 16:00:24 +01:00
> 
> lockdep: Add hrtimer context tracing bits
> 
> Set current->irq_config = 1 for hrtimers which are not marked to expire in
> hard interrupt context during hrtimer_init(). These timers will expire in
> softirq context on PREEMPT_RT.
> 
> Setting this allows lockdep to differentiate these timers. If a timer is
> marked to expire in hard interrupt context then the timer callback is not
> supposed to acquire a regular spinlock instead of a raw_spinlock in the
> expiry callback.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/20200321113242.534508206@linutronix.de
> ---
>  include/linux/irqflags.h | 15 +++++++++++++++
>  include/linux/sched.h    |  1 +
>  kernel/locking/lockdep.c |  2 +-
>  kernel/time/hrtimer.c    |  6 +++++-
>  4 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
> index fdaf286..9c17f9c 100644
> --- a/include/linux/irqflags.h
> +++ b/include/linux/irqflags.h
> @@ -56,6 +56,19 @@ do {						\
>  do {						\
>  	current->softirq_context--;		\
>  } while (0)
> +
> +# define lockdep_hrtimer_enter(__hrtimer)		\
> +	  do {						\
> +		  if (!__hrtimer->is_hard)		\
> +			current->irq_config = 1;	\
> +	  } while (0)
> +
> +# define lockdep_hrtimer_exit(__hrtimer)		\
> +	  do {						\
> +		  if (!__hrtimer->is_hard)		\
> +			current->irq_config = 0;	\
> +	  } while (0)
> +
>  #else
>  # define trace_hardirqs_on()		do { } while (0)
>  # define trace_hardirqs_off()		do { } while (0)
> @@ -68,6 +81,8 @@ do {						\
>  # define trace_hardirq_exit()		do { } while (0)
>  # define lockdep_softirq_enter()	do { } while (0)
>  # define lockdep_softirq_exit()		do { } while (0)
> +# define lockdep_hrtimer_enter(__hrtimer)		do { } while (0)
> +# define lockdep_hrtimer_exit(__hrtimer)		do { } while (0)
>  #endif
>  
>  #if defined(CONFIG_IRQSOFF_TRACER) || \
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 4d3b9ec..933914c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -983,6 +983,7 @@ struct task_struct {
>  	unsigned int			softirq_enable_event;
>  	int				softirqs_enabled;
>  	int				softirq_context;
> +	int				irq_config;

There really need to be some explanation/comment/symbols to clarify
what this field is about and the meaning of the values it can take.

Thanks.