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

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

[Zqiang]

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>
---
 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

[PATCH] rcu-tasks: Dump rcu tasks status when the boot-test failed

[Zqiang]

This commit adds a dump RCU task status function to rcu tasks tests,
used to obtain more information to help debug when the RCU tasks
boot-time tests failed.

Signed-off-by: Zqiang <qiang.zhang@linux.dev>
---

 syzbot reported the RCU tasks boot-time test failed:
 https://syzkaller.appspot.com/bug?extid=251e9abcdac140e7ec74

 kernel/rcu/tasks.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 7f7d1e636217..d9e1e53f4ccf 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1453,6 +1453,7 @@ struct rcu_tasks_test_desc {
 	const char *name;
 	bool notrun;
 	unsigned long runstart;
+	void (*gp_dbg)(void);
 };
 
 static struct rcu_tasks_test_desc tests[] = {
@@ -1460,6 +1461,8 @@ static struct rcu_tasks_test_desc tests[] = {
 		.name = "call_rcu_tasks()",
 		/* If not defined, the test is skipped. */
 		.notrun = IS_ENABLED(CONFIG_TASKS_RCU),
+		/* Dump rcu tasks status, if test failed. */
+		.gp_dbg = show_rcu_tasks_classic_gp_kthread
 	},
 	{
 		.name = "call_rcu_tasks_trace()",
@@ -1519,6 +1522,8 @@ static int rcu_tasks_verify_self_tests(void)
 		while (tests[i].notrun) {		// still hanging.
 			if (time_after(jiffies, tests[i].runstart + bst)) {
 				pr_err("%s has failed boot-time tests.\n", tests[i].name);
+				if (tests[i].gp_dbg)
+					tests[i].gp_dbg();
 				ret = -1;
 				break;
 			}
-- 
2.17.1

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

[Paul E. McKenney]

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?

							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
>