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Subject[PATCH 4.19] rcu/tree: Mark functions as notrace
Date
This patch and problem analysis is based on v4.19 LTS, but v5.4 LTS
and below seem to be involved.

Hulk Robot reports a softlockup problem, see following logs:
[ 41.463870] watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [ksoftirqd/0:9]
[ 41.509763] Modules linked in:
[ 41.512295] CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 4.19.90 #13
[ 41.516134] Hardware name: linux,dummy-virt (DT)
[ 41.519182] pstate: 80c00005 (Nzcv daif +PAN +UAO)
[ 41.522415] pc : perf_trace_buf_alloc+0x138/0x238
[ 41.525583] lr : perf_trace_buf_alloc+0x138/0x238
[ 41.528656] sp : ffff8000c137e880
[ 41.531050] x29: ffff8000c137e880 x28: ffff20000850ced0
[ 41.534759] x27: 0000000000000000 x26: ffff8000c137e9c0
[ 41.538456] x25: ffff8000ce5c2ae0 x24: ffff200008358b08
[ 41.542151] x23: 0000000000000000 x22: ffff2000084a50ac
[ 41.545834] x21: ffff8000c137e880 x20: 000000000000001c
[ 41.549516] x19: ffff7dffbfdf88e8 x18: 0000000000000000
[ 41.553202] x17: 0000000000000000 x16: 0000000000000000
[ 41.556892] x15: 1ffff00036e07805 x14: 0000000000000000
[ 41.560592] x13: 0000000000000004 x12: 0000000000000000
[ 41.564315] x11: 1fffefbff7fbf120 x10: ffff0fbff7fbf120
[ 41.568003] x9 : dfff200000000000 x8 : ffff7dffbfdf8904
[ 41.571699] x7 : 0000000000000000 x6 : ffff0fbff7fbf121
[ 41.575398] x5 : ffff0fbff7fbf121 x4 : ffff0fbff7fbf121
[ 41.579086] x3 : ffff20000850cdc8 x2 : 0000000000000008
[ 41.582773] x1 : ffff8000c1376000 x0 : 0000000000000100
[ 41.586495] Call trace:
[ 41.588922] perf_trace_buf_alloc+0x138/0x238
[ 41.591912] perf_ftrace_function_call+0x1ac/0x248
[ 41.595123] ftrace_ops_no_ops+0x3a4/0x488
[ 41.597998] ftrace_graph_call+0x0/0xc
[ 41.600715] rcu_dynticks_curr_cpu_in_eqs+0x14/0x70
[ 41.603962] rcu_is_watching+0xc/0x20
[ 41.606635] ftrace_ops_no_ops+0x240/0x488
[ 41.609530] ftrace_graph_call+0x0/0xc
[ 41.612249] __read_once_size_nocheck.constprop.0+0x1c/0x38
[ 41.615905] unwind_frame+0x140/0x358
[ 41.618597] walk_stackframe+0x34/0x60
[ 41.621359] __save_stack_trace+0x204/0x3b8
[ 41.624328] save_stack_trace+0x2c/0x38
[ 41.627112] __kasan_slab_free+0x120/0x228
[ 41.630018] kasan_slab_free+0x10/0x18
[ 41.632752] kfree+0x84/0x250
[ 41.635107] skb_free_head+0x70/0xb0
[ 41.637772] skb_release_data+0x3f8/0x730
[ 41.640626] skb_release_all+0x50/0x68
[ 41.643350] kfree_skb+0x84/0x278
[ 41.645890] kfree_skb_list+0x4c/0x78
[ 41.648595] __dev_queue_xmit+0x1a4c/0x23a0
[ 41.651541] dev_queue_xmit+0x28/0x38
[ 41.654254] ip6_finish_output2+0xeb0/0x1630
[ 41.657261] ip6_finish_output+0x2d8/0x7f8
[ 41.660174] ip6_output+0x19c/0x348
[ 41.663850] mld_sendpack+0x560/0x9e0
[ 41.666564] mld_ifc_timer_expire+0x484/0x8a8
[ 41.669624] call_timer_fn+0x68/0x4b0
[ 41.672355] expire_timers+0x168/0x498
[ 41.675126] run_timer_softirq+0x230/0x7a8
[ 41.678052] __do_softirq+0x2d0/0xba0
[ 41.680763] run_ksoftirqd+0x110/0x1a0
[ 41.683512] smpboot_thread_fn+0x31c/0x620
[ 41.686429] kthread+0x2c8/0x348
[ 41.688927] ret_from_fork+0x10/0x18

Look into above call stack, there is a recursive call in
'ftrace_graph_call', and the direct cause of above recursion is that
'rcu_dynticks_curr_cpu_in_eqs' is traced, see following snippet:
__read_once_size_nocheck.constprop.0
ftrace_graph_call <-- 1. first call
......
rcu_dynticks_curr_cpu_in_eqs
ftrace_graph_call <-- 2. recursive call here!!!

Comparing with mainline kernel, commit ff5c4f5cad33 ("rcu/tree:
Mark the idle relevant functions noinstr") mark related functions as
'noinstr' which implies notrace, noinline and sticks things in the
.noinstr.text section.
Link: https://lore.kernel.org/all/20200416114706.625340212@infradead.org/

But we cannot directly backport that commit, because there seems to be
many prepatches. Instead, marking the functions as 'notrace' where it is
'noinstr' in that commit and mark 'rcu_dynticks_curr_cpu_in_eqs' as
inline look like it resolves the problem.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
kernel/rcu/tree.c | 22 +++++++++++-----------
kernel/rcu/tree_plugin.h | 4 ++--
2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f7e89c989df7..01bc3c1f93f9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -275,7 +275,7 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
* Record entry into an extended quiescent state. This is only to be
* called when not already in an extended quiescent state.
*/
-static void rcu_dynticks_eqs_enter(void)
+static notrace void rcu_dynticks_eqs_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int seq;
@@ -298,7 +298,7 @@ static void rcu_dynticks_eqs_enter(void)
* Record exit from an extended quiescent state. This is only to be
* called from an extended quiescent state.
*/
-static void rcu_dynticks_eqs_exit(void)
+static notrace void rcu_dynticks_eqs_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int seq;
@@ -343,7 +343,7 @@ static void rcu_dynticks_eqs_online(void)
*
* No ordering, as we are sampling CPU-local information.
*/
-bool rcu_dynticks_curr_cpu_in_eqs(void)
+static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

@@ -706,7 +706,7 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*/
-static void rcu_eqs_enter(bool user)
+static notrace void rcu_eqs_enter(bool user)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
@@ -763,7 +763,7 @@ void rcu_idle_enter(void)
* If you add or remove a call to rcu_user_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_user_enter(void)
+notrace void rcu_user_enter(void)
{
lockdep_assert_irqs_disabled();
rcu_eqs_enter(true);
@@ -781,7 +781,7 @@ void rcu_user_enter(void)
* If you add or remove a call to rcu_nmi_exit(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_nmi_exit(void)
+notrace void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

@@ -829,7 +829,7 @@ void rcu_nmi_exit(void)
* If you add or remove a call to rcu_irq_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_irq_exit(void)
+notrace void rcu_irq_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

@@ -864,7 +864,7 @@ void rcu_irq_exit_irqson(void)
* allow for the possibility of usermode upcalls messing up our count of
* interrupt nesting level during the busy period that is just now starting.
*/
-static void rcu_eqs_exit(bool user)
+static notrace void rcu_eqs_exit(bool user)
{
struct rcu_dynticks *rdtp;
long oldval;
@@ -914,7 +914,7 @@ void rcu_idle_exit(void)
* If you add or remove a call to rcu_user_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_user_exit(void)
+void notrace rcu_user_exit(void)
{
rcu_eqs_exit(1);
}
@@ -932,7 +932,7 @@ void rcu_user_exit(void)
* If you add or remove a call to rcu_nmi_enter(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_nmi_enter(void)
+notrace void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
long incby = 2;
@@ -982,7 +982,7 @@ void rcu_nmi_enter(void)
* If you add or remove a call to rcu_irq_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y.
*/
-void rcu_irq_enter(void)
+notrace void rcu_irq_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 5f6de49dc78e..568818bef28f 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2677,7 +2677,7 @@ static void rcu_bind_gp_kthread(void)
}

/* Record the current task on dyntick-idle entry. */
-static void rcu_dynticks_task_enter(void)
+static notrace void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
@@ -2685,7 +2685,7 @@ static void rcu_dynticks_task_enter(void)
}

/* Record no current task on dyntick-idle exit. */
-static void rcu_dynticks_task_exit(void)
+static notrace void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
--
2.32.0
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