linux-kernel - Re: [RFC PATCH 50/86] rcu: TASKS_RCU does not need to depend on PREEMPTION

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Message-ID: <71b83b93-dc68-4c71-972a-5f0ccc3a59da@paulmck-laptop>
Date:   Mon, 20 Nov 2023 16:38:52 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
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        krypton@...ich-teichert.org, rostedt@...dmis.org,
        David.Laight@...lab.com, richard@....at, mjguzik@...il.com
Subject: Re: [RFC PATCH 50/86] rcu: TASKS_RCU does not need to depend on
 PREEMPTION

On Tue, Nov 07, 2023 at 01:57:36PM -0800, Ankur Arora wrote:
> With PREEMPTION being always enabled, we don't need TASKS_RCU
> to be explicitly conditioned on it.
> 
> Suggested-by: Paul E. McKenney <paulmck@...nel.org>
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  arch/Kconfig             | 4 ++--
>  include/linux/rcupdate.h | 4 ----
>  kernel/bpf/Kconfig       | 2 +-
>  kernel/trace/Kconfig     | 4 ++--
>  4 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 05ce60036ecc..f5179b24072c 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -55,7 +55,7 @@ config KPROBES
>  	depends on MODULES
>  	depends on HAVE_KPROBES
>  	select KALLSYMS
> -	select TASKS_RCU if PREEMPTION
> +	select TASKS_RCU
>  	help
>  	  Kprobes allows you to trap at almost any kernel address and
>  	  execute a callback function.  register_kprobe() establishes
> @@ -104,7 +104,7 @@ config STATIC_CALL_SELFTEST
>  config OPTPROBES
>  	def_bool y
>  	depends on KPROBES && HAVE_OPTPROBES
> -	select TASKS_RCU if PREEMPTION
> +	select TASKS_RCU
>  
>  config KPROBES_ON_FTRACE
>  	def_bool y
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 5e5f920ade90..7246ee602b0b 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -171,10 +171,6 @@ static inline void rcu_nocb_flush_deferred_wakeup(void) { }
>  	} while (0)
>  void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
>  void synchronize_rcu_tasks(void);
> -# else
> -# define rcu_tasks_classic_qs(t, preempt) do { } while (0)
> -# define call_rcu_tasks call_rcu
> -# define synchronize_rcu_tasks synchronize_rcu
>  # endif
>  
>  # ifdef CONFIG_TASKS_TRACE_RCU
> diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> index 6a906ff93006..e3231b28e2a0 100644
> --- a/kernel/bpf/Kconfig
> +++ b/kernel/bpf/Kconfig
> @@ -27,7 +27,7 @@ config BPF_SYSCALL
>  	bool "Enable bpf() system call"
>  	select BPF
>  	select IRQ_WORK
> -	select TASKS_RCU if PREEMPTION
> +	select TASKS_RCU
>  	select TASKS_TRACE_RCU
>  	select BINARY_PRINTF
>  	select NET_SOCK_MSG if NET
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 61c541c36596..e090387b1c2d 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -163,7 +163,7 @@ config TRACING
>  	select BINARY_PRINTF
>  	select EVENT_TRACING
>  	select TRACE_CLOCK
> -	select TASKS_RCU if PREEMPTION
> +	select TASKS_RCU
>  
>  config GENERIC_TRACER
>  	bool
> @@ -204,7 +204,7 @@ config FUNCTION_TRACER
>  	select GENERIC_TRACER
>  	select CONTEXT_SWITCH_TRACER
>  	select GLOB
> -	select TASKS_RCU if PREEMPTION
> +	select TASKS_RCU
>  	select TASKS_RUDE_RCU
>  	help
>  	  Enable the kernel to trace every kernel function. This is done
> -- 
> 2.31.1
>