On Tue, May 19, 2026 at 09:01:28PM +0200, Arnd Bergmann wrote: > From: Arnd Bergmann <[email protected]> > > 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. > > Signed-off-by: Arnd Bergmann <[email protected]>
Reviewed-by: Paul E. McKenney <[email protected]> > --- > kernel/rcu/tree_nocb.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index 1047b30cd46b..373b877cf171 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; > -- > 2.39.5 >
