[PATCH rcu 0/2] Tasks RCU updates for v6.5

[PATCH rcu 0/2] Tasks RCU updates for v6.5

[Paul E. McKenney]

Hello!

This series contains Tasks RCU updates.

1.	rcu-tasks: Avoid pr_info() with spin lock in
	cblist_init_generic(), courtesy of Shigeru Yoshida.

2.	rcu-tasks: Clarify the cblist_init_generic() function's pr_info()
	output, courtesy of Zqiang.

An additional Tasks RCU update may instead be found here due to
conflict-inducing dependencies:

https://lore.kernel.org/all/20230510165832.2187453-8-paulmck@kernel.org/

						Thanx, Paul

------------------------------------------------------------------------

 b/kernel/rcu/tasks.h |    5 ++++-
 kernel/rcu/tasks.h   |    6 ++----
 2 files changed, 6 insertions(+), 5 deletions(-)

[PATCH rcu 1/2] rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()

[Paul E. McKenney]

From: Shigeru Yoshida <syoshida@redhat.com>

pr_info() is called with rtp->cbs_gbl_lock spin lock locked.  Because
pr_info() calls printk() that might sleep, this will result in BUG
like below:

[    0.206455] cblist_init_generic: Setting adjustable number of callback queues.
[    0.206463]
[    0.206464] =============================
[    0.206464] [ BUG: Invalid wait context ]
[    0.206465] 5.19.0-00428-g9de1f9c8ca51 #5 Not tainted
[    0.206466] -----------------------------
[    0.206466] swapper/0/1 is trying to lock:
[    0.206467] ffffffffa0167a58 (&port_lock_key){....}-{3:3}, at: serial8250_console_write+0x327/0x4a0
[    0.206473] other info that might help us debug this:
[    0.206473] context-{5:5}
[    0.206474] 3 locks held by swapper/0/1:
[    0.206474]  #0: ffffffff9eb597e0 (rcu_tasks.cbs_gbl_lock){....}-{2:2}, at: cblist_init_generic.constprop.0+0x14/0x1f0
[    0.206478]  #1: ffffffff9eb579c0 (console_lock){+.+.}-{0:0}, at: _printk+0x63/0x7e
[    0.206482]  #2: ffffffff9ea77780 (console_owner){....}-{0:0}, at: console_emit_next_record.constprop.0+0x111/0x330
[    0.206485] stack backtrace:
[    0.206486] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-00428-g9de1f9c8ca51 #5
[    0.206488] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014
[    0.206489] Call Trace:
[    0.206490]  <TASK>
[    0.206491]  dump_stack_lvl+0x6a/0x9f
[    0.206493]  __lock_acquire.cold+0x2d7/0x2fe
[    0.206496]  ? stack_trace_save+0x46/0x70
[    0.206497]  lock_acquire+0xd1/0x2f0
[    0.206499]  ? serial8250_console_write+0x327/0x4a0
[    0.206500]  ? __lock_acquire+0x5c7/0x2720
[    0.206502]  _raw_spin_lock_irqsave+0x3d/0x90
[    0.206504]  ? serial8250_console_write+0x327/0x4a0
[    0.206506]  serial8250_console_write+0x327/0x4a0
[    0.206508]  console_emit_next_record.constprop.0+0x180/0x330
[    0.206511]  console_unlock+0xf7/0x1f0
[    0.206512]  vprintk_emit+0xf7/0x330
[    0.206514]  _printk+0x63/0x7e
[    0.206516]  cblist_init_generic.constprop.0.cold+0x24/0x32
[    0.206518]  rcu_init_tasks_generic+0x5/0xd9
[    0.206522]  kernel_init_freeable+0x15b/0x2a2
[    0.206523]  ? rest_init+0x160/0x160
[    0.206526]  kernel_init+0x11/0x120
[    0.206527]  ret_from_fork+0x1f/0x30
[    0.206530]  </TASK>
[    0.207018] cblist_init_generic: Setting shift to 1 and lim to 1.

This patch moves pr_info() so that it is called without
rtp->cbs_gbl_lock locked.

Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Tested-by: "Zhang, Qiang1" <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tasks.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 5f4fc8184dd0..65df1aaf0ce9 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -241,7 +241,6 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 	if (rcu_task_enqueue_lim < 0) {
 		rcu_task_enqueue_lim = 1;
 		rcu_task_cb_adjust = true;
-		pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
 	} else if (rcu_task_enqueue_lim == 0) {
 		rcu_task_enqueue_lim = 1;
 	}
@@ -272,6 +271,10 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 		raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
 	}
 	raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
+
+	if (rcu_task_cb_adjust)
+		pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
+
 	pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
 }
 
-- 
2.40.1

[PATCH rcu 2/2] rcu-tasks: Clarify the cblist_init_generic() function's pr_info() output

[Paul E. McKenney]

From: Zqiang <qiang1.zhang@intel.com>

This commit uses rtp->name instead of __func__ and outputs the value
of rcu_task_cb_adjust, thus reducing console-log output.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 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 65df1aaf0ce9..cf7b00af9474 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -272,10 +272,8 @@ static void cblist_init_generic(struct rcu_tasks *rtp)
 	}
 	raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
 
-	if (rcu_task_cb_adjust)
-		pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
-
-	pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
+	pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name,
+			data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust);
 }
 
 // IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic().
-- 
2.40.1