rcu: add rcu_read_lock_dont_migrate()

migrate_disable() is called to disable migration in the kernel, and it is
often used together with rcu_read_lock().

However, with PREEMPT_RCU disabled, it's unnecessary, as rcu_read_lock()
will always disable preemption, which will also disable migration.

Introduce rcu_read_lock_dont_migrate() and rcu_read_unlock_migrate(),
which will do the migration enable and disable only when PREEMPT_RCU.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20250821090609.42508-2-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 120536f4c6eb1d8f91afc16111d976f7a14ef4fc..9691ca380a4fe1b02bbd075d9cf3fcdc24086a6a 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -962,6 +962,20 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
        preempt_enable_notrace();
 }
 
+static __always_inline void rcu_read_lock_dont_migrate(void)
+{
+       if (IS_ENABLED(CONFIG_PREEMPT_RCU))
+               migrate_disable();
+       rcu_read_lock();
+}
+
+static inline void rcu_read_unlock_migrate(void)
+{
+       rcu_read_unlock();
+       if (IS_ENABLED(CONFIG_PREEMPT_RCU))
+               migrate_enable();
+}
+
 /**
  * RCU_INIT_POINTER() - initialize an RCU protected pointer
  * @p: The pointer to be initialized.