Re: Regression in next with use printk_safe buffers in printk

[Tony Lindgren <tony@atomide.com>]

* Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> [170215 17:32]:
> On (02/15/17 10:01), Tony Lindgren wrote:
> [..]
> > Below is another issue I noticed caused by commit f975237b7682 that
> > I noticed during booting.
> 
> do you mean that with f975237b7682 you _always_ see that illegal RCU
> usage warning?

Yeah on every boot on devices using cpuidle_coupled.

> > 8< --------------------------
> > [    2.581939] hw-breakpoint: Failed to enable monitor mode on CPU 0.
> > [    2.591613] hw-breakpoint: CPU 0 failed to disable vector catch
> > [    2.597686]
> > [    2.597717] ===============================
> > [    2.597717] [ ERR: suspicious RCU usage.  ]
> > [    2.597717] 4.10.0-rc8-next-20170215+ #119 Not tainted
> > [    2.597717] -------------------------------
> > [    2.597717] ./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage!
> 
> so this is trace_console(text, len) from
> 
> 	cpuidle_enter_state()
> 	...
> 		vprintk_emit()		<< error: Failed to enable monitor mode/CPU 0 failed to disable...
> 		  console_unlock()
> 		    call_console_drivers()
> 		      trace_console()
> 
> 
> > [    2.597717]
> > [    2.597717] other info that might help us debug this:
> > [    2.597717]
> > [    2.597717]
> > [    2.597717] RCU used illegally from idle CPU!
> 
> um... is this what rcuidle() for?

Yeah I think that's all there is to it. We've had a bunch of similar
issues pop up over past year :) See for example:

$ git log --author=McKenney drivers/base/power

> ---
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 7180088cbb23..34da86e73d00 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1563,7 +1563,7 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
>  {
>  	struct console *con;
>  
> -	trace_console(text, len);
> +	trace_console_rcuidle(text, len);
>  
>  	if (!console_drivers)
>  		return;
> 
> ---
> 
> 
> I need to look more at this.

That fixes it for me thanks, so feel free to add:

Tested-by: Tony Lindgren <tony@atomide.com>


> > [    2.597717] rcu_scheduler_active = 2, debug_locks = 0
> > [    2.597747] RCU used illegally from extended quiescent state!
> 
> 
> > [    2.597747] 2 locks held by swapper/0/0:
> > [    2.597747]  #0:  (cpu_pm_notifier_lock){......}, at: [<c0237e2c>] cpu_pm_exit+0x10/0x54
> > [    2.597747]  #1:  (console_lock){+.+.+.}, at: [<c01ab350>] vprintk_emit+0x264/0x474
> > [    2.597747]
> > [    2.597747] stack backtrace:
> > [    2.597778] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119
> > [    2.597778] Hardware name: Generic OMAP4 (Flattened Device Tree)
> > [    2.597778] [<c0110228>] (unwind_backtrace) from [<c010c224>] (show_stack+0x10/0x14)
> > [    2.597778] [<c010c224>] (show_stack) from [<c04ca8a0>] (dump_stack+0xac/0xe0)
> > [    2.597778] [<c04ca8a0>] (dump_stack) from [<c01ab084>] (console_unlock+0x5e8/0x650)
> > [    2.597778] [<c01ab084>] (console_unlock) from [<c01ab35c>] (vprintk_emit+0x270/0x474)
> > [    2.597778] [<c01ab35c>] (vprintk_emit) from [<c01ab6f0>] (vprintk_default+0x20/0x28)
> > [    2.597808] [<c01ab6f0>] (vprintk_default) from [<c0250c94>] (printk+0x20/0x30)
> > [    2.597808] [<c0250c94>] (printk) from [<c0111004>] (reset_ctrl_regs+0x108/0x288)
> > [    2.597808] [<c0111004>] (reset_ctrl_regs) from [<c0111220>] (dbg_cpu_pm_notify+0x28/0x30)
> > [    2.597808] [<c0111220>] (dbg_cpu_pm_notify) from [<c015f3ac>] (notifier_call_chain+0x44/0x80)
> > [    2.597808] [<c015f3ac>] (notifier_call_chain) from [<c0237e48>] (cpu_pm_exit+0x2c/0x54)
> > [    2.597808] [<c0237e48>] (cpu_pm_exit) from [<c0126ca0>] (omap_enter_idle_coupled+0x80/0x208)
> > [    2.597808] [<c0126ca0>] (omap_enter_idle_coupled) from [<c0680d80>] (cpuidle_enter_state+0x118/0x4ac)
> > [    2.597808] [<c0680d80>] (cpuidle_enter_state) from [<c0682e54>] (cpuidle_enter_state_coupled+0x3a8/0x40c)
> > [    2.597839] [<c0682e54>] (cpuidle_enter_state_coupled) from [<c0190c04>] (do_idle+0x1a4/0x218)
> > [    2.597839] [<c0190c04>] (do_idle) from [<c0190ffc>] (cpu_startup_entry+0x18/0x1c)
> > [    2.597839] [<c0190ffc>] (cpu_startup_entry) from [<c0c00c40>] (start_kernel+0x35c/0x3d4)
> > [    2.597839] [<c0c00c40>] (start_kernel) from [<8000807c>] (0x8000807c)