Re: [PATCH] rcu-tasks: Remove unused struct rcu_tasks's->n_ipis_fails variables

["Zqiang" <qiang.zhang@linux.dev>]

> 
> On Mon, Jul 06, 2026 at 06:03:09PM +0800, Zqiang wrote:
> 
> > 
> > The RCU tasks trace has been reimplemented by 'commit c27cea4416a3
> >  ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")', the
> >  rcu_tasks structure's->n_ipis_fails is no longer used, this commit
> >  therefore remove it.
> >  
> >  Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> > 
> I have queued both for review and testing, thank you!
> 
> This patch produced the expected result in my initial tests. However,
> for the second patch, I used this command to force a stall:
> 
> tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 15 --configs "TASKS01 TASKS02 TASKS03 RUDE01" --bootargs "rcutorture.stall_cpu=660" --trust-make
> 
> Except I got vanilla RCU CPU stall warnings, but not RCU Tasks nor
> RCU Tasks Rude stall warnings. And not even the "grace period number"
> pre-stall message. Probably because I am forgetting something. But what
> did you do to test your change?

Hello, Paul

The rcutorture module use module_init() to load, however the
rcu_tasks_initiate_self_tests() is called in core_initcall(), 
the core_initcall() have a higher priority than module_init().

This is possible, the RCU tasks test may have already completed, 
but the rcutorture may have only just started.

so I use the following modifications to verify:

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index d9e1e53f4ccf..7e5ff5108cdd 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1489,7 +1489,6 @@ static void rcu_tasks_initiate_self_tests(void)
        pr_info("Running RCU Tasks wait API self tests\n");
        tests[0].runstart = jiffies;
        synchronize_rcu_tasks();
-       call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
 #endif
 
 #ifdef CONFIG_TASKS_RUDE_RCU
@@ -1555,6 +1554,7 @@ static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused)
 static int rcu_tasks_verify_schedule_work(void)
 {
        INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn);
+       call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
        rcu_tasks_verify_work_fn(NULL);
        return 0;
 }



Run qemu with bootparams="rcutorture.torture_type=srcu 
rcutorture.stall_cpu=800 rcutorture.stall_cpu_block=1 
rcutorture.stall_no_softlockup=1 rcupdate.rcu_tasks_lazy_ms=120000"

[   30.826022] call_rcu_tasks() has failed boot-time tests.
[   30.826790] rcu_tasks: RTGS_WAIT_CBS(11) since 7596 g:4 i:0 kCuU l:30000 
[   30.827424] ------------[ cut here ]------------
[   30.827862] WARNING: kernel/rcu/tasks.h:1533 at rcu_tasks_verify_self_tests+0xa7/0xc0, CPU#1: kworker/1:1/79
[   30.828717] Modules linked in:
[   30.829144] CPU: 1 UID: 0 PID: 79 Comm: kworker/1:1 Tainted: G        W           7.1.0-rc4+ #25 PREEMPT(lazy)  e641c8af833b714510f82b4c2bc5dbbb1ef1e911
[   30.830176] Tainted: [W]=WARN 
[   30.830468] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   30.831326] Workqueue: events rcu_tasks_verify_work_fn
....
[  722.218096] INFO: rcu_tasks detected stalls on tasks:
[  722.218689] 0000000095041800: .. nvcsw: 2/2 holdout: 1 idle_cpu: -1/7
[  722.219308] task:rcu_torture_sta state:R  running task     stack:0     pid:122   tgid:122   ppid:2      task_flags:0x208040 flags:0x00080000
[  722.220442] Call Trace:
[  722.220744]  <TASK>
[  722.221035]  __schedule+0x2e9/0x1460
[  722.221449]  ? preempt_schedule+0x30/0x40
[  722.221895]  preempt_schedule_common+0x24/0x90
[  722.222432]  preempt_schedule+0x30/0x40
[  722.222842]  rcu_torture_stall+0x266/0x430
[  722.223286]  ? __kthread_parkme+0x8f/0xe0
[  722.223735]  ? __pfx_rcu_torture_stall+0x10/0x10
[  722.224226]  kthread+0x13d/0x180
[  722.224600]  ? __pfx_kthread+0x10/0x10
[  722.224996]  ret_from_fork+0x29d/0x3b0
[  722.225669]  ? __pfx_kthread+0x10/0x10
[  722.226131]  ret_from_fork_asm+0x1a/0x30
[  722.226668]  </TASK>


Thanks
Zqiang


> 
>  Thanx, Paul
> 
> > 
> > ---
> >  kernel/rcu/tasks.h | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >  
> >  diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> >  index f4da5fad70f5..7f7d1e636217 100644
> >  --- a/kernel/rcu/tasks.h
> >  +++ b/kernel/rcu/tasks.h
> >  @@ -67,7 +67,6 @@ struct rcu_tasks_percpu {
> >  * @gp_start: Most recent grace-period start in jiffies.
> >  * @tasks_gp_seq: Number of grace periods completed since boot in upper bits.
> >  * @n_ipis: Number of IPIs sent to encourage grace periods to end.
> >  - * @n_ipis_fails: Number of IPI-send failures.
> >  * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
> >  * @lazy_jiffies: Number of jiffies to allow callbacks to be lazy.
> >  * @pregp_func: This flavor's pre-grace-period function (optional).
> >  @@ -102,7 +101,6 @@ struct rcu_tasks {
> >  unsigned long gp_start;
> >  unsigned long tasks_gp_seq;
> >  unsigned long n_ipis;
> >  - unsigned long n_ipis_fails;
> >  struct task_struct *kthread_ptr;
> >  unsigned long lazy_jiffies;
> >  rcu_tasks_gp_func_t gp_func;
> >  @@ -735,12 +733,12 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
> >  if (havecbs && haveurgent && haveurgentcbs)
> >  break;
> >  }
> >  - pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c%c%c l:%lu %s\n",
> >  + pr_info("%s: %s(%d) since %lu g:%lu i:%lu %c%c%c%c l:%lu %s\n",
> >  rtp->kname,
> >  tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
> >  jiffies - data_race(rtp->gp_jiffies),
> >  data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
> >  - data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
> >  + data_race(rtp->n_ipis),
> >  ".k"[!!data_race(rtp->kthread_ptr)],
> >  ".C"[havecbs],
> >  ".u"[haveurgent],
> >  -- 
> >  2.17.1
> >
>