On Thu, Jul 23, 2026 at 06:04:30PM +0800, Zqiang wrote:
> When CONFIG_KASAN=y and CONFIG_KASAN_STACK=y builds, the
> show_rcu_gp_kthreads() exceeds the 1024-byte frame-size limit:
>
> make kernel/rcu/tree.o KCFLAGS="-fstack-usage"
> DESCEND objtool
> DESCEND bpf/resolve_btfids
> INSTALL libsubcmd_headers
> CC kernel/rcu/tree.o
> In file included from kernel/rcu/tree.c:4998:
> kernel/rcu/tree_stall.h: In function 'show_rcu_gp_kthreads':
> kernel/rcu/tree_stall.h:994:1: warning: the frame size of 1656 bytes is
> larger than 1024 bytes [-Wframe-larger-than=]
>
> grep show_rcu kernel/rcu/tree.su
> tree_nocb.h:1622:13:show_rcu_nocb_state 896 dynamic,bounded
> tree_stall.h:933:6:show_rcu_gp_kthreads 1784 dynamic,bounded
> tree_stall.h:1102:13:sysrq_show_rcu 16 static
>
> Wrap the pr_info() into two noinline_for_stack helpers function:
> show_rcu_state() print rcu_state status, and show_rcu_node()
> print single rcu_node status.
>
> After apply this change:
>
> grep show_rcu kernel/rcu/tree.su
> tree_stall.h:955:22:show_rcu_node 696 dynamic,bounded
> tree_stall.h:930:22:show_rcu_state 872 dynamic,bounded
> tree_nocb.h:1622:13:show_rcu_nocb_state 896 dynamic,bounded
> tree_stall.h:972:6:show_rcu_gp_kthreads 544 static
> tree_stall.h:1113:13:sysrq_show_rcu 16 static
>
> Signed-off-by: Zqiang <[email protected]>
Queued and pushed for further review and testing, thank you!
Thanx, Paul
> ---
> kernel/rcu/tree_stall.h | 47 +++++++++++++++++++++++++----------------
> 1 file changed, 29 insertions(+), 18 deletions(-)
>
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 45b9856ccd2b..a6dfd036a7e9 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -927,20 +927,13 @@ bool rcu_check_boost_fail(unsigned long gp_state, int
> *cpup)
> }
> EXPORT_SYMBOL_GPL(rcu_check_boost_fail);
>
> -/*
> - * Show the state of the grace-period kthreads.
> - */
> -void show_rcu_gp_kthreads(void)
> +static noinline_for_stack void show_rcu_state(void)
> {
> - unsigned long cbs = 0;
> - int cpu;
> unsigned long j;
> unsigned long ja;
> unsigned long jr;
> unsigned long js;
> unsigned long jw;
> - struct rcu_data *rdp;
> - struct rcu_node *rnp;
> struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
>
> j = jiffies;
> @@ -957,21 +950,39 @@ void show_rcu_gp_kthreads(void)
> (long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)),
> data_race(READ_ONCE(rcu_state.gp_max)),
> data_race(READ_ONCE(rcu_state.gp_flags)));
> +}
> +
> +static noinline_for_stack void show_rcu_node(struct rcu_node *rnp)
> +{
> + pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask
> %#lx %c%c%c%c ->n_boosts %ld\n",
> + rnp->grplo, rnp->grphi,
> + (long)data_race(READ_ONCE(rnp->gp_seq)),
> + (long)data_race(READ_ONCE(rnp->gp_seq_needed)),
> + data_race(READ_ONCE(rnp->qsmask)),
> + ".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))],
> + ".B"[!!data_race(READ_ONCE(rnp->boost_tasks))],
> + ".E"[!!data_race(READ_ONCE(rnp->exp_tasks))],
> + ".G"[!!data_race(READ_ONCE(rnp->gp_tasks))],
> + data_race(READ_ONCE(rnp->n_boosts)));
> +}
> +
> +/*
> + * Show the state of the grace-period kthreads.
> + */
> +void show_rcu_gp_kthreads(void)
> +{
> + unsigned long cbs = 0;
> + int cpu;
> + struct rcu_data *rdp;
> + struct rcu_node *rnp;
> +
> + show_rcu_state();
> rcu_for_each_node_breadth_first(rnp) {
> if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
> READ_ONCE(rnp->gp_seq_needed)) &&
> !data_race(READ_ONCE(rnp->qsmask)) &&
> !data_race(READ_ONCE(rnp->boost_tasks)) &&
> !data_race(READ_ONCE(rnp->exp_tasks)) &&
> !data_race(READ_ONCE(rnp->gp_tasks)))
> continue;
> - pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld
> ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n",
> - rnp->grplo, rnp->grphi,
> - (long)data_race(READ_ONCE(rnp->gp_seq)),
> - (long)data_race(READ_ONCE(rnp->gp_seq_needed)),
> - data_race(READ_ONCE(rnp->qsmask)),
> - ".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))],
> - ".B"[!!data_race(READ_ONCE(rnp->boost_tasks))],
> - ".E"[!!data_race(READ_ONCE(rnp->exp_tasks))],
> - ".G"[!!data_race(READ_ONCE(rnp->gp_tasks))],
> - data_race(READ_ONCE(rnp->n_boosts)));
> + show_rcu_node(rnp);
> if (!rcu_is_leaf_node(rnp))
> continue;
> for_each_leaf_node_possible_cpu(rnp, cpu) {
> --
> 2.17.1
>
