[PATCH v3] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

[Zqiang]

Currently, the srcu_gp_start_if_needed() is always be invoked in
preempt disable's critical section, this commit therefore remove
redundant preempt_disable/enable() in srcu_gp_start_if_needed()
and adds a call to lockdep_assert_preemption_disabled() in order
to enable lockdep to diagnose mistaken invocations of this function
from preempts-enabled code.

Fixes: 65b4a59557f6 ("srcu: Make Tiny SRCU explicitly disable preemption")
Signed-off-by: Zqiang <qiang.zh...@linux.dev>
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
 kernel/rcu/srcutiny.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index b52ec45698e8..3450c3751ef7 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct srcu_struct 
*ssp)
 {
        unsigned long cookie;
 
-       preempt_disable();  // Needed for PREEMPT_LAZY
+       lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY
        cookie = get_state_synchronize_srcu(ssp);
        if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
-               preempt_enable();
                return;
        }
        WRITE_ONCE(ssp->srcu_idx_max, cookie);
@@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
                else if (list_empty(&ssp->srcu_work.entry))
                        list_add(&ssp->srcu_work.entry, &srcu_boot_list);
        }
-       preempt_enable();
 }
 
 /*
-- 
2.48.1