[PATCH] rcu: Avoid tracing a few functions executed in stop machine

[Ronald Monthero <debug.penguin32@gmail.com>]

[upstream commit 48f8070f5dd8]
This backport patch for kernel 5.15v is derived from upstream
48f8070f5dd8. On 5.15 kernel it fixes recurring oops in context of rcu
detected stalls, indicated below.

log :
root@ls1021atwr:~# uname -r
5.15.93-rt58+ge0f69a158d5b
oops dump stack

** ID_531 main/smp_fsm.c:1884 <inrcu: INFO: rcu_preempt detected
stalls on CPUs/tasks:   <<< [1]
rcu:    Tasks blocked on level-0 rcu_node (CPUs 0-1): P116/2:b..l
        (detected by 1, t=2102 jiffies, g=12741, q=1154)
task:irq/31-arm-irq1 state:D stack: 0 pid:116 ppid:2 flags:0x00000000
[<8064b97f>] (__schedule) from [<8064bb01>] (schedule+0x8d/0xc2)
[<8064bb01>] (schedule) from [<8064fa65>] (schedule_timeout+0x6d/0xa0)
[<8064fa65>] (schedule_timeout) from [<804ba353>]
(fsl_ifc_run_command+0x6f/0x178)
[<804ba353>] (fsl_ifc_run_command) from [<804ba72f>]
(fsl_ifc_cmdfunc+0x203/0x2b8)
[<804ba72f>] (fsl_ifc_cmdfunc) from [<804b135f>]
....
< snipped >

rcu: rcu_preempt kthread timer wakeup didn't happen for 764 jiffies!
g12741 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x1000
rcu:    Possible timer handling issue on cpu=0 timer-softirq=1095
rcu: rcu_preempt kthread starved for 765 jiffies! g12741 f0x0
RCU_GP_WAIT_FQS(5) ->state=0x1000 ->cpu=0    <<< [2]
rcu:    Unless rcu_preempt kthread gets sufficient CPU time, OOM is
now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:D stack: 0 pid: 13 ppid:     2 flags:0x00000000
[<8064b97f>] (__schedule) from [<8064ba03>] (schedule_rtlock+0x1b/0x2e)
[<8064ba03>] (schedule_rtlock) from [<8064ea6f>]
(rtlock_slowlock_locked+0x93/0x108)
[<8064ea6f>] (rtlock_slowlock_locked) from [<8064eb1b>]
[<8064eb1b>] (rt_spin_lock) from [<8021b723>] (__local_bh_disable_ip+0x6b/0x110)
[<8021b723>] (__local_bh_disable_ip) from [<8025a90f>]
(del_timer_sync+0x7f/0xe0)
[<8025a90f>] (del_timer_sync) from [<8064fa6b>] (schedule_timeout+0x73/0xa0)
Exception stack(0x820fffb0 to 0x820ffff8)
rcu: Stack dump where RCU GP kthread last ran:
...
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
<  .. >

Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
---
 kernel/rcu/tree_plugin.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d070059163d7..36ca6bacd430 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -458,7 +458,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
  * be quite short, for example, in the case of the call from
  * rcu_read_unlock_special().
  */
-static void
+static notrace void
 rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 {
 	bool empty_exp;
@@ -578,7 +578,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
  * is disabled.  This function cannot be expected to understand these
  * nuances, so the caller must handle them.
  */
-static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
+static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
 	return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
 		READ_ONCE(t->rcu_read_unlock_special.s)) &&
@@ -592,7 +592,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
  * evaluate safety in terms of interrupt, softirq, and preemption
  * disabling.
  */
-static void rcu_preempt_deferred_qs(struct task_struct *t)
+static notrace void rcu_preempt_deferred_qs(struct task_struct *t)
 {
 	unsigned long flags;
 
@@ -922,7 +922,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
  * Because there is no preemptible RCU, there can be no deferred quiescent
  * states.
  */
-static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
+static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
 {
 	return false;
 }
-- 
2.34.1