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rcu/nocb: reduce stack usage in nocb_gp_wait()

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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 <chentao@kylinos.cn>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit is contained in:
Arnd Bergmann 2026-05-19 21:01:28 +02:00 committed by Uladzislau Rezki (Sony)
parent 42c5468f9c
commit 002668809b
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/tree_nocb.h
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@ -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;