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

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Date:   Mon, 18 Apr 2022 17:12:23 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.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: [PATCH rcu 02/12] rcu: Make the TASKS_RCU Kconfig option be selected

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.

[ 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