From: Zqiang <qiang.zhang@linux.dev>
To: paulmck@kernel.org, frederic@kernel.org,
neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com,
urezki@gmail.com, boqun@kernel.org
Cc: qiang.zhang@linux.dev, rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] rcu: Reduce stack usage in show_rcu_gp_kthreads()
Date: Thu, 23 Jul 2026 18:04:30 +0800 [thread overview]
Message-ID: <20260723100430.17813-1-qiang.zhang@linux.dev> (raw)
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 <qiang.zhang@linux.dev>
---
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
next reply other threads:[~2026-07-23 10:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-23 10:04 Zqiang [this message]
2026-07-23 18:30 ` Paul E. McKenney
2026-07-24 13:20 ` David Laight
2026-07-24 18:11 ` Paul E. McKenney
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