Re: [PATCH] tracing: Do not synchronize freeing of trigger filter on boot up

[Steven Rostedt]

On Wed, 14 Dec 2022 12:03:33 -0800
"Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:

> > > Avoid calling the synchronization function when system_state is
> > > SYSTEM_BOOTING.  
> > 
> > Shouldn't this be done inside tracepoint_synchronize_unregister()?
> > Then, it will prevent similar warnings if we expand boot time feature.  
> 
> How about the following wide-spectrum fix within RCU_LOCKDEP_WARN()?
> Just in case there are ever additional issues of this sort?

Adding more tracing command line parameters is triggering this more. I now
hit:

[    0.213442] rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
[    0.214653] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=8
[    0.232023] ------------[ cut here ]------------
[    0.232704] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:1410 rcu_poll_gp_seq_start_unlocked+0x8a/0xa0
[    0.234241] Modules linked in:
[    0.234715] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.1.0-rc6-test-00046-ga0ca17bfe724-dirty #63
[    0.236069] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
[    0.237549] RIP: 0010:rcu_poll_gp_seq_start_unlocked+0x8a/0xa0
[    0.238495] Code: 02 0f 0b 48 89 ee 5b 48 c7 c7 00 ca b1 b3 5d e9 cc 0f c1 00 65 8b 05 85 f3 dd 4d 85 c0 75 a1 65 8b 05 d6 f0 dd 4d 85 c0 75 96 <0f> 0b eb 92 5b 5d e9 eb 18 fc 00 66 66 2e 0f 1f 84 00 00 00 00 00
[    0.241433] RSP: 0000:ffffffffb3a03d28 EFLAGS: 00010046
[    0.242289] RAX: 0000000000000000 RBX: ffffffffb3bcfc48 RCX: 0000000000000001
[    0.243355] RDX: 0000000080000001 RSI: 0000000000000001 RDI: ffffffffb3bcfc48
[    0.244421] RBP: 0000000000000000 R08: ffff97a3c012b8f8 R09: fffffffffffffffe
[    0.245569] R10: ffffffffb3a03e78 R11: 00000000ffffffff R12: 0000000000000040
[    0.246752] R13: ffffffffb3a30500 R14: ffffffffb3be6180 R15: ffff97a3c0355d10
[    0.247826] FS:  0000000000000000(0000) GS:ffff97a537c00000(0000) knlGS:0000000000000000
[    0.249084] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.250012] CR2: ffff97a51e201000 CR3: 000000025c826001 CR4: 00000000000606b0
[    0.251122] Call Trace:
[    0.251491]  <TASK>
[    0.251810]  synchronize_rcu+0xb6/0x1e0
[    0.252393]  ? smp_call_function_many_cond+0x36d/0x3b0
[    0.253243]  ? enable_trace_buffered_event+0x10/0x10
[    0.254021]  trace_buffered_event_disable+0x7c/0x140
[    0.254786]  __ftrace_event_enable_disable+0x11c/0x250
[    0.255559]  __ftrace_set_clr_event_nolock+0xe3/0x130
[    0.256321]  ftrace_set_clr_event+0x9a/0xe0
[    0.256976]  early_enable_events+0x64/0xa8
[    0.257647]  trace_event_init+0xd6/0x2dd
[    0.258305]  start_kernel+0x760/0x9e0
[    0.258862]  secondary_startup_64_no_verify+0xe5/0xeb
[    0.259634]  </TASK>
[    0.259966] irq event stamp: 0
[    0.260427] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
[    0.261448] hardirqs last disabled at (0): [<0000000000000000>] 0x0
[    0.262424] softirqs last  enabled at (0): [<0000000000000000>] 0x0
[    0.263402] softirqs last disabled at (0): [<0000000000000000>] 0x0
[    0.264345] ---[ end trace 0000000000000000 ]---
[    0.265088] ------------[ cut here ]------------

Where kernel/rcu/tree.c:1410 is at:

// Make the polled API aware of the beginning of a grace period, but
// where caller does not hold the root rcu_node structure's lock.
static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
{
	unsigned long flags;
	struct rcu_node *rnp = rcu_get_root();

	if (rcu_init_invoked()) {
		lockdep_assert_irqs_enabled(); <<-------------- 1410
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
	}
	rcu_poll_gp_seq_start(snap);
	if (rcu_init_invoked())
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}


-- Steve