From: Arnd Bergmann Date: Tue, 19 May 2026 19:01:28 +0000 (+0200) Subject: rcu/nocb: reduce stack usage in nocb_gp_wait() X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=002668809b068c528838c1ab1ff46c87bdbb095d;p=thirdparty%2Flinux.git rcu/nocb: reduce stack usage in nocb_gp_wait() When CONFIG_UBSAN_ALIGNMENT is enabled, the stack usage of nocb_gp_wait() grows above typical warning limits: In file included from kernel/rcu/tree.c:4930: kernel/rcu/tree_nocb.h: In function 'rcu_nocb_gp_kthread': kernel/rcu/tree_nocb.h:866:1: error: the frame size of 1968 bytes is larger than 1280 bytes [-Werror=frame-larger-than=] Apparently, the problem is passing rcu_data from a 'void *' pointer, which gcc assumes may be misaligned. When the function is not inlined into rcu_nocb_gp_kthread(), that is no longer visible to gcc. Add a 'noinline_for_stack' annotation that leads to skipping a lot of the alignment sanitizer checks and keeps the stack usage 60% lower here. Reviewed-by: Kunwu Chan Reviewed-by: Frederic Weisbecker Reviewed-by: Paul E. McKenney Signed-off-by: Arnd Bergmann Signed-off-by: Uladzislau Rezki (Sony) --- diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 1047b30cd46b7..373b877cf171d 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -655,7 +655,7 @@ static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu) * No-CBs GP kthreads come here to wait for additional callbacks to show up * or for grace periods to end. */ -static void nocb_gp_wait(struct rcu_data *my_rdp) +static noinline_for_stack void nocb_gp_wait(struct rcu_data *my_rdp) { bool bypass = false; int __maybe_unused cpu = my_rdp->cpu;