linux-kernel - Re: [PATCH][RFC] lockdep: improve comments in wait-type checks

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Message-ID: <YRM5heBfgNtEGvoC@boqun-archlinux>
Date:   Wed, 11 Aug 2021 10:44:21 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Zhouyi Zhou <zhouzhouyi@...il.com>
Cc:     peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, paulmck@...nel.org, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: [PATCH][RFC] lockdep: improve comments in wait-type checks

Hi,

On Wed, Aug 11, 2021 at 05:03:19AM +0800, Zhouyi Zhou wrote:
> Hi Peter,
>   I think comments in wait-type checks may benifit from some comments
> improvement.

Thanks for looking into this!

Even for an RFC patch, it's better that you write a proper commit log,
and note that you can put all this background information right after
the "---" line, if you think that will help people review it.

>   I recklessly add Paul to signed-off-by, because I asked his opinion
> about comment in rcu_read_lock_bh part.
> 

Probably a Suggested-by will suffice, but I leave that to Paul ;-)

> Thanks a lot
> Zhouyi
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@...il.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

Please make you the last one in the "Signed-off-by" list, see
Documentation/process/submitting-patches.rst:

"Notably, the last Signed-off-by: must always be that of the developer
submitting the patch."

Regards,
Boqun

> ---
>  include/linux/lockdep_types.h | 2 +-
>  kernel/locking/lockdep.c      | 2 +-
>  kernel/rcu/update.c           | 4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
> index 3e726ace5c62..d22430840b53 100644
> --- a/include/linux/lockdep_types.h
> +++ b/include/linux/lockdep_types.h
> @@ -21,7 +21,7 @@ enum lockdep_wait_type {
>  	LD_WAIT_SPIN,		/* spin loops, raw_spinlock_t etc.. */
>  
>  #ifdef CONFIG_PROVE_RAW_LOCK_NESTING
> -	LD_WAIT_CONFIG,		/* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
> +	LD_WAIT_CONFIG,		/* preemptible in PREEMPT_RT, spinlock_t etc.. */
>  #else
>  	LD_WAIT_CONFIG = LD_WAIT_SPIN,
>  #endif
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index bf1c00c881e4..952d0ccf8776 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4671,7 +4671,7 @@ print_lock_invalid_wait_context(struct task_struct *curr,
>  /*
>   * Verify the wait_type context.
>   *
> - * This check validates we takes locks in the right wait-type order; that is it
> + * This check validates we take locks in the right wait-type order; that is it
>   * ensures that we do not take mutexes inside spinlocks and do not attempt to
>   * acquire spinlocks inside raw_spinlocks and the sort.
>   *
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index c21b38cc25e9..690b0cec7459 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -247,7 +247,7 @@ struct lockdep_map rcu_lock_map = {
>  	.name = "rcu_read_lock",
>  	.key = &rcu_lock_key,
>  	.wait_type_outer = LD_WAIT_FREE,
> -	.wait_type_inner = LD_WAIT_CONFIG, /* XXX PREEMPT_RCU ? */
> +	.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT implies PREEMPT_RCU */
>  };
>  EXPORT_SYMBOL_GPL(rcu_lock_map);
>  
> @@ -256,7 +256,7 @@ struct lockdep_map rcu_bh_lock_map = {
>  	.name = "rcu_read_lock_bh",
>  	.key = &rcu_bh_lock_key,
>  	.wait_type_outer = LD_WAIT_FREE,
> -	.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_LOCK also makes BH preemptible */
> +	.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */
>  };
>  EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
>  
> -- 
> 2.25.1
>