linux-kernel - Re: [PATCH 02/10] rcu: Move rcu_preempt_depth

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Message-Id: <769AEAAB-7DEA-4D94-8979-F01EDFD6EE46@joelfernandes.org>
Date: Sun, 31 Mar 2024 16:39:54 +0530
From: Joel Fernandes <joel@...lfernandes.org>
To: Lai Jiangshan <jiangshanlai@...il.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org, x86@...nel.org,
 Lai Jiangshan <jiangshan.ljs@...group.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <quic_neeraju@...cinc.com>,
 Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH 02/10] rcu: Move rcu_preempt_depth_set() to rcupdate.h

> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@...il.com> wrote:
> 
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> Prepare for arch-specific-defined rcu_preempt_depth_set().
> 
> No functionality change intended, but it has to be defined as a macro
> as rcupdate.h is a very low level header included from areas that don't
> even know about the task struct "current".

Sorry I did not follow changelog. If some rcupdate.h includers do not know
about task_struct, how does adding a macro that uses current help?

Thanks,

 - Joel

> 
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Frederic Weisbecker <frederic@...nel.org>
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> ---
> include/linux/rcupdate.h | 1 +
> kernel/rcu/tree_plugin.h | 5 -----
> 2 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 16f519914415..210f65baf47c 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -78,6 +78,7 @@ void __rcu_read_unlock(void);
>  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
>  */
> #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
> +#define rcu_preempt_depth_set(val) WRITE_ONCE(current->rcu_read_lock_nesting, (val))
> 
> #else /* #ifdef CONFIG_PREEMPT_RCU */
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 36a8b5dbf5b5..b1264096d03a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -387,11 +387,6 @@ static int rcu_preempt_read_exit(void)
>    return ret;
> }
> 
> -static void rcu_preempt_depth_set(int val)
> -{
> -    WRITE_ONCE(current->rcu_read_lock_nesting, val);
> -}
> -
> /*
>  * Preemptible RCU implementation for rcu_read_lock().
>  * Just increment ->rcu_read_lock_nesting, shared state will be updated
> --
> 2.19.1.6.gb485710b
>