linux-kernel - Re: [PATCH 4/5] rcu-tasks: Fix read-side primitives comment for call_rcu_tasks

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Message-ID: <20210818154642.GT4126399@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 18 Aug 2021 08:46:42 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Neeraj Upadhyay <neeraju@...eaurora.org>
Cc:     josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, urezki@...il.com,
        frederic@...nel.org, boqun.feng@...il.com
Subject: Re: [PATCH 4/5] rcu-tasks: Fix read-side primitives comment for
 call_rcu_tasks_trace

On Wed, Aug 18, 2021 at 12:58:42PM +0530, Neeraj Upadhyay wrote:
> call_rcu_tasks_trace() does have read-side primitives - rcu_read_lock_trace()
> and rcu_read_unlock_trace(). Fix this information in the comments.
> 
> Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
> ---
>  kernel/rcu/tasks.h | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 244e06a..5f9c14c 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1214,13 +1214,9 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t)
>   *
>   * The callback function will be invoked some time after a full grace
>   * period elapses, in other words after all currently executing RCU
> - * read-side critical sections have completed. call_rcu_tasks_trace()
> - * assumes that the read-side critical sections end at context switch,
> - * cond_resched_rcu_qs(), or transition to usermode execution.  As such,
> - * there are no read-side primitives analogous to rcu_read_lock() and
> - * rcu_read_unlock() because this primitive is intended to determine
> - * that all tasks have passed through a safe state, not so much for
> - * data-structure synchronization.
> + * read-side critical sections have completed. These read-side

The above line should start "Tasks Trace read-side critical..." for
the benefit of people who stop reading before the next sentence.  :-/

							Thanx, Paul

> + * critical sections are delimited by calls to rcu_read_lock_trace()
> + * and rcu_read_unlock_trace().
>   *
>   * See the description of call_rcu() for more detailed information on
>   * memory ordering guarantees.
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, 
> hosted by The Linux Foundation
>