Merge branch 'bpf-introduce-and-use-rcu_read_lock_dont_migrate'

Menglong Dong says:

====================
bpf: introduce and use rcu_read_lock_dont_migrate

migrate_disable() and rcu_read_lock() are used to together in many case in
bpf. However, when PREEMPT_RCU is not enabled, rcu_read_lock() will
disable preemption, which indicate migrate_disable(), so we don't need to
call it in this case.

In this series, we introduce rcu_read_lock_dont_migrate and
rcu_read_unlock_migrate, which will call migrate_disable and
migrate_enable only when PREEMPT_RCU enabled. And use
rcu_read_lock_dont_migrate in bpf subsystem.

Changes since V2:
* make rcu_read_lock_dont_migrate() more compatible by using IS_ENABLED()

Changes since V1:
* introduce rcu_read_lock_dont_migrate() instead of
  rcu_migrate_disable() + rcu_read_lock()
====================

Link: https://patch.msgid.link/20250821090609.42508-1-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>