linux-kernel - Re: hrtimer_interrupt::pr_warn_once() causes BUG: Invalid wait context

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Date:   Wed, 20 Jan 2021 13:52:43 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: hrtimer_interrupt::pr_warn_once() causes BUG: Invalid wait
 context

On 01/14/21 12:45, Qais Yousef wrote:
> Hi
> 
> I hit this splat today
> 
> 	# [67628.388606] hrtimer: interrupt took 304720 ns
> 	[67628.393546]
> 	[67628.393550] =============================
> 	[67628.393554] [ BUG: Invalid wait context ]
> 	[67628.393557] 5.11.0-rc3-00019-g86be331946f7 #37 Not tainted
> 	[67628.393560] -----------------------------
> 	[67628.393563] sugov:0/192 is trying to lock:
> 	[67628.393566] ffff000800b1d898 (&port_lock_key){-.-.}-{3:3}, at: pl011_console_write+0x138/0x218
> 	[67628.393581] other info that might help us debug this:
> 	[67628.393584] context-{2:2}
> 	[67628.393586] 4 locks held by sugov:0/192:
> 	[67628.393589]  #0: ffff0008059cb720 (&sg_policy->work_lock){+.+.}-{4:4}, at: sugov_work+0x58/0x88
> 	[67628.393603]  #1: ffff800015446f20 (prepare_lock){+.+.}-{4:4}, at: clk_prepare_lock+0x34/0xb0
> 	[67628.393618]  #2: ffff8000152aaa60 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0x12c/0x310
> 	[67628.393632]  #3: ffff8000152aab88 (console_owner){-.-.}-{0:0}, at: console_unlock+0x190/0x6d8
> 	[67628.393646] stack backtrace:
> 	[67628.393649] CPU: 0 PID: 192 Comm: sugov:0 Not tainted 5.11.0-rc3-00019-g86be331946f7 #37
> 	[67628.393653] Hardware name: ARM Juno development board (r2) (DT)
> 	[67628.393656] Call trace:
> 	[67628.393659]  dump_backtrace+0x0/0x1b0
> 	[67628.393661]  show_stack+0x20/0x70
> 	[67628.393664]  dump_stack+0xf8/0x168
> 	[67628.393666]  __lock_acquire+0x964/0x1c88
> 	[67628.393669]  lock_acquire+0x26c/0x500
> 	[67628.393671]  _raw_spin_lock+0x64/0x88
> 	[67628.393674]  pl011_console_write+0x138/0x218
> 	[67628.393677]  console_unlock+0x2c4/0x6d8
> 	[67628.393680]  vprintk_emit+0x134/0x310
> 	[67628.393682]  vprintk_default+0x40/0x50
> 	[67628.393685]  vprintk_func+0xfc/0x2b0
> 	[67628.393687]  printk+0x68/0x90
> 	[67628.393690]  hrtimer_interrupt+0x24c/0x250
> 	[67628.393693]  arch_timer_handler_phys+0x3c/0x50
> 	[67628.393695]  handle_percpu_devid_irq+0xd8/0x460
> 	[67628.393698]  generic_handle_irq+0x38/0x50
> 	[67628.393701]  __handle_domain_irq+0x6c/0xc8
> 	[67628.393704]  gic_handle_irq+0xb0/0xf0
> 	[67628.393706]  el1_irq+0xb4/0x180
> 	[67628.393709]  _raw_spin_unlock_irqrestore+0x58/0xa8
> 	[67628.393712]  hrtimer_start_range_ns+0x1b0/0x420
> 	[67628.393715]  msg_submit+0x100/0x108
> 	[67628.393717]  mbox_send_message+0x84/0x128
> 	[67628.393720]  scpi_send_message+0x11c/0x2a8
> 	[67628.393723]  scpi_dvfs_set_idx+0x48/0x70
> 	[67628.393726]  scpi_dvfs_set_rate+0x60/0x78
> 	[67628.393728]  clk_change_rate+0x184/0x8a8
> 	[67628.393731]  clk_core_set_rate_nolock+0x1c0/0x280
> 	[67628.393734]  clk_set_rate+0x40/0x98
> 	[67628.393736]  scpi_cpufreq_set_target+0x40/0x68
> 	[67628.393739]  __cpufreq_driver_target+0x1a0/0x5d0
> 
> AFAICT the call to pr_warn_once() is how we end up here. Not sure if there's an
> appropriate or easy fix for that.

Oh I just accidentally came across printk_deferred_once() which looks like the
right thing to do. I can't reproduce but I'll send a patch over the weekend to
see if anyone will complain why it shouldn't work.

Thanks

--
Qais Yousef