[PATCH v6 01/14] rcu-tasks-trace: Let TASKS_TRACE_RCU_NO_MB default on without RCU_EXPERT

[Josef Bacik]

TASKS_TRACE_RCU_NO_MB defaults to ARCH_WANTS_NO_INSTR, on the grounds
(see 1a72f4bb6f3e) that architectures with noinstr entry code only ever
run tracing where RCU is watching and so can dispense with the read-side
smp_mb() in rcu_read_lock_trace() and friends.  But the option also
depends on RCU_EXPERT, and a Kconfig default is not applied to a symbol
whose dependencies are unmet, so on an ordinary RCU_EXPERT=n build of
such an architecture the option is simply absent and every Tasks Trace
reader pays for two full barriers that the architecture does not need.

Keep the prompt behind RCU_EXPERT, so that overriding the default in
either direction remains an expert decision, but let the default itself
apply unconditionally.  On x86-64 and arm64 defconfig this turns the
barriers off, as intended; architectures without ARCH_WANTS_NO_INSTR
are unchanged.

Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 kernel/rcu/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 332df7a7a634..e3cfe1fe5592 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -142,8 +142,8 @@ config TASKS_TRACE_RCU
 	default n
 
 config TASKS_TRACE_RCU_NO_MB
-	bool "Override RCU Tasks Trace inclusion of read-side memory barriers"
-	depends on RCU_EXPERT && TASKS_TRACE_RCU
+	bool "Override RCU Tasks Trace inclusion of read-side memory barriers" if RCU_EXPERT
+	depends on TASKS_TRACE_RCU
 	default ARCH_WANTS_NO_INSTR
 	help
 	  This option prevents the use of read-side memory barriers in

-- 
2.55.0