linux-kernel - Re: [PATCH rcu 02/12] rcu: Make the TASKS

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Date:   Tue, 19 Apr 2022 23:13:58 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, rostedt@...dmis.org,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Zhouyi Zhou <zhouzhouyi@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH rcu 02/12] rcu: Make the TASKS_RCU Kconfig option be
 selected

On Mon, 18 Apr 2022 17:12:23 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> Currently, any kernel built with CONFIG_PREEMPTION=y also gets
> CONFIG_TASKS_RCU=y, which is not helpful to people trying to build
> preemptible kernels of minimal size.
> 
> Because CONFIG_TASKS_RCU=y is needed only in kernels doing tracing of
> one form or another, this commit moves from TASKS_RCU deciding when it
> should be enabled to the tracing Kconfig options explicitly selecting it.
> This allows building preemptible kernels without TASKS_RCU, if desired.
> 
> This commit also updates the SRCU-N and TREE09 rcutorture scenarios
> in order to avoid Kconfig errors that would otherwise result from
> CONFIG_TASKS_RCU being selected without its CONFIG_RCU_EXPERT dependency
> being met.

Thanks for fixing this dependency.

This looks good to me (for kprobe part)

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you,

> 
> [ paulmck: Apply BPF_SYSCALL feedback from Andrii Nakryiko. ]
> 
> Reported-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> Tested-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> Tested-by: Zhouyi Zhou <zhouzhouyi@...il.com>
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> --- Update SRCU-N and TREE09 to avoid Kconfig errors.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  arch/Kconfig                                          | 1 +
>  kernel/bpf/Kconfig                                    | 1 +
>  kernel/rcu/Kconfig                                    | 3 ++-
>  kernel/trace/Kconfig                                  | 1 +
>  tools/testing/selftests/rcutorture/configs/rcu/SRCU-N | 2 ++
>  tools/testing/selftests/rcutorture/configs/rcu/TREE09 | 2 ++
>  6 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 29b0167c088b..1bf29ce754af 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -35,6 +35,7 @@ config KPROBES
>  	depends on MODULES
>  	depends on HAVE_KPROBES
>  	select KALLSYMS
> +	select TASKS_RCU if PREEMPTION
>  	help
>  	  Kprobes allows you to trap at almost any kernel address and
>  	  execute a callback function.  register_kprobe() establishes
> diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> index d56ee177d5f8..2dfe1079f772 100644
> --- a/kernel/bpf/Kconfig
> +++ b/kernel/bpf/Kconfig
> @@ -27,6 +27,7 @@ config BPF_SYSCALL
>  	bool "Enable bpf() system call"
>  	select BPF
>  	select IRQ_WORK
> +	select TASKS_RCU if PREEMPTION
>  	select TASKS_TRACE_RCU
>  	select BINARY_PRINTF
>  	select NET_SOCK_MSG if NET
> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index f559870fbf8b..4f665ae0cf55 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -78,7 +78,8 @@ config TASKS_RCU_GENERIC
>  	  task-based RCU implementations.  Not for manual selection.
>  
>  config TASKS_RCU
> -	def_bool PREEMPTION
> +	def_bool 0
> +	select IRQ_WORK
>  	help
>  	  This option enables a task-based RCU implementation that uses
>  	  only voluntary context switch (not preemption!), idle, and
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 2c43e327a619..bf5da6c4e999 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -144,6 +144,7 @@ config TRACING
>  	select BINARY_PRINTF
>  	select EVENT_TRACING
>  	select TRACE_CLOCK
> +	select TASKS_RCU if PREEMPTION
>  
>  config GENERIC_TRACER
>  	bool
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N
> index 2da8b49589a0..07f5e0a70ae7 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N
> @@ -6,3 +6,5 @@ CONFIG_PREEMPT_NONE=y
>  CONFIG_PREEMPT_VOLUNTARY=n
>  CONFIG_PREEMPT=n
>  #CHECK#CONFIG_RCU_EXPERT=n
> +CONFIG_KPROBES=n
> +CONFIG_FTRACE=n
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE09 b/tools/testing/selftests/rcutorture/configs/rcu/TREE09
> index 8523a7515cbf..fc45645bb5f4 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE09
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE09
> @@ -13,3 +13,5 @@ CONFIG_DEBUG_LOCK_ALLOC=n
>  CONFIG_RCU_BOOST=n
>  CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
>  #CHECK#CONFIG_RCU_EXPERT=n
> +CONFIG_KPROBES=n
> +CONFIG_FTRACE=n
> -- 
> 2.31.1.189.g2e36527f23
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>