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

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Date:   Tue, 19 Apr 2022 07:25:23 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Masami Hiramatsu <mhiramat@...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>
Subject: Re: [PATCH rcu 02/12] rcu: Make the TASKS_RCU Kconfig option be
 selected

On Tue, Apr 19, 2022 at 11:13:58PM +0900, Masami Hiramatsu wrote:
> 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!  I will apply this on my next rebase.

							Thanx, Paul

> 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>