linux-kernel - [PATCH rcu 12/18] rcu: Make rcu_gp_init() and rcu_gp_fqs

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Message-Id: <20210721202127.2129660-12-paulmck@kernel.org>
Date:   Wed, 21 Jul 2021 13:21:20 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Rong Chen <rong.a.chen@...el.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH rcu 12/18] rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack

The kbuild test project found an oversized stack frame in rcu_gp_kthread()
for some kernel configurations.  This oversizing was due to a very large
amount of inlining, which is unnecessary due to the fact that this code
executes infrequently.  This commit therefore marks rcu_gp_init() and
rcu_gp_fqs_loop noinline_for_stack to conserve stack space.

Reported-by: kernel test robot <lkp@...el.com>
Tested-by: Rong Chen <rong.a.chen@...el.com>
[ paulmck: noinline_for_stack per Nathan Chancellor. ]
Reviewed-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bc6ccf0ba3b24..e472c78036011 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1739,7 +1739,7 @@ static void rcu_strict_gp_boundary(void *unused)
 /*
  * Initialize a new grace period.  Return false if no grace period required.
  */
-static bool rcu_gp_init(void)
+static noinline_for_stack bool rcu_gp_init(void)
 {
 	unsigned long firstseq;
 	unsigned long flags;
@@ -1933,7 +1933,7 @@ static void rcu_gp_fqs(bool first_time)
 /*
  * Loop doing repeated quiescent-state forcing until the grace period ends.
  */
-static void rcu_gp_fqs_loop(void)
+static noinline_for_stack void rcu_gp_fqs_loop(void)
 {
 	bool first_gp_fqs;
 	int gf = 0;
-- 
2.31.1.189.g2e36527f23