Patch "rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()" has been added to the 6.4-stable tree

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This is a note to let you know that I've just added the patch titled

    rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rcu-tasks-avoid-pr_info-with-spin-lock-in-cblist_ini.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1e5233c6acc983e4260bd78c410a36f74d547a9f
Author: Shigeru Yoshida <syoshida@xxxxxxxxxx>
Date:   Wed Aug 3 01:22:05 2022 +0900

    rcu-tasks: Avoid pr_info() with spin lock in cblist_init_generic()
    
    [ Upstream commit 5fc8cbe4cf0fd34ded8045c385790c3bf04f6785 ]
    
    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@xxxxxxxxxx>
    Tested-by: "Zhang, Qiang1" <qiang1.zhang@xxxxxxxxx>
    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 8f08c087142b0..9b9ce09f8f358 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));
 }
 



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