[PATCH RFC 10/16] rcu: Remove unused func parameter from callback-enqueue functions

From: Joel Fernandes <[email protected]>

Ever since the kvfree_rcu() tracing moved out of the callback-enqueue
path, rcutree_enqueue() no longer looks at the callback function
pointer:  By the time it is invoked, __call_rcu_common() has already
stored the function into rhp->func, and the enqueue path only adds
the rcu_head to the segmented callback list and emits tracepoints
that do not take the function pointer.

Nevertheless, the function pointer is still threaded through
call_rcu_core(), call_rcu_nocb(), and rcutree_enqueue(), forcing
each level to carry a dead argument.

Remove the parameter from all three functions, from the no-CBs stub,
and from the corresponding declarations.  Anything needing the
callback function can still get it from rhp->func.

No functional change.

Signed-off-by: Joel Fernandes <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
 kernel/rcu/tree.c      | 10 +++++-----
 kernel/rcu/tree.h      |  2 +-
 kernel/rcu/tree_nocb.h |  6 +++---
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 91d5b4dd08bf5c..390dad82675db5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3024,7 +3024,7 @@ static int __init rcu_spawn_core_kthreads(void)
 	return 0;
 }
 
-static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func)
+static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head)
 {
 	rcu_segcblist_enqueue(&rdp->cblist, head);
 	trace_rcu_callback(rcu_state.name, head,
@@ -3036,9 +3036,9 @@ static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_cal
  * Handle any core-RCU processing required by a call_rcu() invocation.
  */
 static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
-			  rcu_callback_t func, unsigned long flags)
+			  unsigned long flags)
 {
-	rcutree_enqueue(rdp, head, func);
+	rcutree_enqueue(rdp, head);
 	/*
 	 * If called from an extended quiescent state, invoke the RCU
 	 * core in order to force a re-evaluation of RCU's idleness.
@@ -3179,9 +3179,9 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
 	check_cb_ovld(rdp);
 
 	if (unlikely(rcu_rdp_is_offloaded(rdp)))
-		call_rcu_nocb(rdp, head, func, flags, lazy);
+		call_rcu_nocb(rdp, head, flags, lazy);
 	else
-		call_rcu_core(rdp, head, func, flags);
+		call_rcu_core(rdp, head, flags);
 	local_irq_restore(flags);
 }
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 587bd71396eaa3..ca88aaa29d615e 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -507,7 +507,7 @@ static bool wake_nocb_gp(struct rcu_data *rdp);
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 				  unsigned long j, bool lazy);
 static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
-			  rcu_callback_t func, unsigned long flags, bool lazy);
+			  unsigned long flags, bool lazy);
 static void __maybe_unused __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
 						unsigned long flags);
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 373b877cf171d3..95dbf33462a2ff 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -603,13 +603,13 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 }
 
 static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
-			  rcu_callback_t func, unsigned long flags, bool lazy)
+			  unsigned long flags, bool lazy)
 {
 	bool was_alldone;
 
 	if (!rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) {
 		/* Not enqueued on bypass but locked, do regular enqueue */
-		rcutree_enqueue(rdp, head, func);
+		rcutree_enqueue(rdp, head);
 		__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
 	}
 }
@@ -1666,7 +1666,7 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 }
 
 static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
-			  rcu_callback_t func, unsigned long flags, bool lazy)
+			  unsigned long flags, bool lazy)
 {
 	WARN_ON_ONCE(1);  /* Should be dead code! */
 }
-- 
2.40.1